JPH0429602B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing expanded graphite. More specifically, the present invention relates to a method for producing expanded graphite suitable for use as a material for graphite products having shapes such as sheet, tape, ring, and block shapes. Conventionally, expanded graphite is produced by immersing natural graphite, hardwood graphite, or pyrolytic graphite in an oxidizing bath consisting of concentrated sulfuric acid and concentrated nitric acid at an appropriate temperature for an appropriate period of time, as described in Japanese Patent Publication No. 44-23966. The wet graphite particles (hereinafter often referred to simply as wet graphite particles), that is, the graphite intercalation compound, obtained by
It is obtained by heating to a temperature of 1000°C and expanding it 100 to 300 times in the C-axis direction (direction perpendicular to the carbon layer). The low bulk density expanded graphite obtained in this way has the heat resistance, chemical resistance, and lubricity inherent to graphite.
In addition, it is well known that it is used for gaskets, packing, etc. because it can be compression molded or roll molded into sheets or rings without using any adhesives or adhesives. . Generally, wet graphite particles are prepared using oxidizing media containing concentrated sulfuric acid at very high concentrations of 95-98%, such as concentrated sulfuric acid and nitric acid, perchloric acid, chromic acid, potassium permanganate, iodic acid, or periodic acid. It is often obtained by oxidation treatment with an oxidizing agent that is a combination of the above, particularly a typical oxidizing agent that is an oxidizing medium consisting of concentrated nitric acid or perchloric acid and concentrated sulfuric acid. All of these methods involve various operational hazards because they use highly concentrated sulfuric acid, and it is difficult to dispose of the highly concentrated oxidizing medium used, resulting in a large cost burden.
Economic efficiency is also bad. In addition, flexible graphite products made by pressure-molding caterpillar-shaped expanded graphite obtained by heating and expanding wet graphite particles obtained by the above method using concentrated sulfuric acid, nitric acid, or perchloric acid do not contain sulfur, nitrogen, or chlorine. Remaining compounds cannot be avoided. This is due to the fact that the expansion process of the oxidized wet graphite particles is carried out rapidly in a short period of time, albeit at a high temperature. be done. Even if expanded graphite is heat-treated for a long time in a temperature range where it is not oxidized by oxygen in the air in order to remove these compounds, complete removal is difficult and uneconomical. Moreover, when the graphite molded product is applied to a sealing material, the sulfur, nitrogen, or chlorine compounds remaining in graphite destroy or dissolve the corrosion-resistant passive film of the metal it comes into contact with, such as stainless steel, resulting in pitting corrosion or crevice corrosion. This causes and promotes problems, which poses a practical problem. In addition, these residual elements have the disadvantage of causing unfavorable results when graphite products are applied to electrochemical applications such as electrodes. As a method to improve the various drawbacks associated with the above-mentioned chemical immersion method, graphite bisulfate, which is a graphite intercalation compound, is electrolytically oxidized in an electrolytic bath using concentrated sulfuric acid or concentrated nitric acid as an electrolyte, using graphite as an anode. A method has been proposed in which expanded graphite is obtained by obtaining a salt or nitrate and heating and expanding it. In this method, the concentration of sulfuric acid, etc., can be lower than that in the immersion method, and there is no need to additionally use a strong oxidizing agent, which causes various problems. Also, special public service in 1982-
As disclosed in the specification of No. 18532, a graphite intercalation compound is generated by using graphite as a cathode in an electrolytic solution containing an acid that reacts with graphite to form a graphite intercalation compound, and then the generated graphite intercalation compound is A method has been proposed for producing expanded graphite by subjecting a compound obtained by electrolytic reduction as a cathode to expel excess acid from between graphite layers to heat treatment for expansion. However, even in the above two methods of manufacturing expanded graphite in which graphite intercalation compounds obtained by electrolysis are expanded, residual sulfur compounds and nitrogen compounds in the expanded graphite cannot be avoided, and the expanded graphite obtained by the dipping method cannot be avoided. Like graphite, when applied to sealing materials, etc., it is undesirable because it corrodes contact metals. As is clear from the above explanation, in all of the above conventional methods, strong acids such as concentrated sulfuric acid, concentrated nitric acid, and perchloric acid are used. The treatment of SO _x , NO _x or chlorine compound gases in the waste gas generated during this process is a problem in terms of pollution control. Therefore, the investment amount for auxiliary equipment such as pollution equipment is large and the cost becomes high. As a method to improve the various drawbacks of the method using strong acids described above, a graphite ternary intercalation compound consisting of an alkali metal selected from potassium, lithium, rubidium, and cesium, an organic molecule such as tetrahydrofuran, and graphite is heated and expanded to form expanded graphite. A method for obtaining is presented in Japanese Patent Application Laid-Open No. 156515/1983.
This method is a method for producing expanded graphite that does not contain sulfur compounds, chlorine compounds, or nitrogen compounds that cause metal rust, and also does not require pollution prevention. However, the alkali metal used in this method has a high market price, and high manufacturing costs are unavoidable. Furthermore, the intercalation compound consisting of potassium, tetrahydrofuran and graphite used in the above method cannot be produced in the atmosphere;
Generally, the operation must be carried out under an inert gas such as nitrogen or argon. Therefore, high manufacturing costs cannot be avoided. Therefore, the present inventors have conducted extensive research to solve the above problems, and as a result, they have arrived at the present invention. Therefore, one object of the present invention is to provide an economical manufacturing method that can produce expanded graphite that does not contain sulfur compounds, chlorine compounds, or nitrogen compounds that cause metal rust, and that is inexpensive. Another object of the present invention is to provide a method for producing expanded graphite that does not require expensive pollution control equipment. Furthermore, another object of the present invention is to provide a method for producing expanded graphite that can be produced at a lower heating temperature than conventional methods and that can recover and reuse substances inserted between graphite layers. It is to provide. These and other objects, features and benefits will become apparent from the detailed description provided below. According to the present invention, a graphite ternary intercalation compound consisting of sodium, tetrahydrofuran and graphite and/or
Alternatively, there is provided a method for producing expanded graphite, which comprises heating and expanding the residual compound thereof. The graphite ternary intercalation compound (hereinafter often simply referred to as the "ternary intercalation compound") made of sodium, tetrahydrofuran, and graphite used in the present invention and its residual compound (hereinafter often simply referred to as the "residual compound") will be explained. . The ternary intercalation compound used in the present invention and its residual compounds are represented by C _x Na (THF) _y . here
THF stands for tetrahydrofuran. x is generally x≧10, preferably 72≧x≧10. Further, y is 3≧y>0 in the case of a ternary intercalation compound, and 1>y>0 in the case of a residual compound of the ternary intercalation compound, and a residual compound with 1>y>0.1 is preferably used. The method for producing the ternary intercalation compound used in the present invention is as follows. First, in the first step, either anthracene or benzophenone and metallic sodium are placed in tetrahydrofuran to cause a reaction. At this time, the reaction can be carried out either by leaving the reaction system stationary or by stirring it. The reaction temperature at this time is generally -10 to 50℃, the reaction can be carried out in air, and the pressure is generally
It is 0.8~10 atm. The reaction time is generally 12 to 24 hours when left standing, but can be shortened by stirring. Next, graphite was added to the reaction solution obtained in the second step, and the temperature was the same as above.
After stirring under pressure and atmospheric conditions, the mixture is allowed to stand for 12 to 24 hours to obtain a ternary intercalation compound. At this time, the standing time can be shortened by sufficiently stirring. The amounts of raw materials used in the above reaction are generally 0.014 to 0.50 mol of sodium metal, 0.014 to 0.50 mol of anthracene or benzophenone, and 0.014 to 10 mol of tetrahydrofuran per mol of carbon in graphite. however,
It is preferable to use 0.056 mol or more of tetrahydrofuran. Although the mechanism of the reaction that generates the ternary intercalation compound is not clear, it is presumed as follows. First of all, each of the following formulas: It is thought that a sodium-anthracene complex and a sodium-benzophenone complex represented by these are formed, and then sodium and tetrahydrofuran invade between the graphite layers. Another method for producing the ternary intercalation compound used in the present invention is to introduce either anthracene or benzophenone, metallic sodium and graphite into tetrahydrofuran almost simultaneously in the atmosphere,
There is also a method of stirring and reacting in air at a temperature of -10 to 50°C and a pressure of 0.8 to 10 atm. Generally after stirring 12
The desired product is obtained by leaving for ~24 hours, but the standing time can be shortened by appropriately selecting stirring conditions. The amount of raw materials is the same as in the above method. In this method, anthracene or benzophenone, metallic sodium, and graphite are introduced into tetrahydrofuran almost simultaneously, but the reaction is thought to proceed in the same order as described above. The graphite used to produce the ternary intercalation compound used in the method of the present invention is obtained by subjecting graphitizable carbon such as natural graphite, petroleum coke, coal coke, pitch coke, etc. to heat treatment for graphitization. Ordinary artificial graphite, cache graphite, or pyrolytic graphite is used. When manufacturing, it is used in the form of graphite powder, and its shape can be either scaly or granular, and the particle size is finer than 20 meshes (Tyler), preferably 20 to 500 meshes (Tyler). be able to. Commercially available sodium metal, anthracene, benzophenone, and tetrahydrofuran, which are raw materials for producing the ternary intercalation compound used in the method of the present invention, can be used. The above-mentioned residual compounds used in the method of the present invention are:
It is obtained by leaving a graphite ternary intercalation compound consisting of sodium, tetrahydrofuran and graphite in air at room temperature. The residual compound is obtained by the gradual decomposition of the ternary intercalation compound by moisture in the air, and its composition is not constant. Although it depends on the humidity in the air, in general, it is preferably used in the method of the present invention if it is allowed to stand for up to about one week. Another method for obtaining residual compounds is to further in air after the ternary intercalation compound is formed.
There is a method of stirring the obtained solution of the ternary intercalation compound at a temperature of -10 to 50°C to obtain the residual compound. In this method, moisture in the air enters the solution, and it is thought that the ternary intercalation compound decomposes and becomes a residual compound under the influence of the moisture. Still another method for obtaining the residual compound is to obtain the residual compound by adding water and stirring in air at a temperature of -10 to 50° C. after forming the ternary intercalation compound. Preferred examples of the ternary intercalation compound used in the present invention include C ₃₂ Na (THF) ₃ , C ₆₄ Na (THF) and C ₇₂ Na (THF), and preferred examples of the remaining compounds include the above three Examples include residual compounds of the original intercalation compound. The heating temperature in the present invention is 100 to 1400°C, preferably 200 to 1000°C. Any heating device may be used as long as the above temperature can be obtained. Generally, an electric furnace is used. Also, the heating time is 2
The heating time is 60 seconds, preferably 10 to 30 seconds, and heating can be carried out at normal pressure. The degree of expansion of graphite in the present invention is 10 times or more, preferably 80 to 400 times. In the present invention, by selecting appropriate heating temperature conditions, etc., sodium vapor and tetrahydrofuran vapor generated during heating expansion can be recovered and reused using a cold trap. The commercial price of the sodium used in the present invention is 10 to 20 times lower than that of conventional potassium, and the manufacturing cost is low. Therefore, the manufacturing cost is lower than using lithium, rubidium, and cesium, which are more expensive than potassium. It's much more advantageous. Furthermore, the ternary intercalation compound used in the present invention is
It is not necessary to react under an inert gas such as N ₂ or argon, and it can be produced in air. The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to the scope of the Examples. Reference Example 1 1.2 g of finely chopped metallic sodium and 9.3 g of anthracene were added together to 50 ml of tetrahydrofuran which had been thoroughly dehydrated with a molecular sieve, and the mixture was allowed to stand at room temperature for 24 hours in an open atmosphere. then in the air
Scaly graphite from Madagascar with a broad peak in particle size distribution between 50 and 80 meshes (Tyler), dried at 110°C, with a size of 24 to 200 meshes (Tyler)
Add 10 g of C ₃₂ Na (THF) ₃ , stir gently with the reaction container stoppered, and leave it at room temperature for 24 hours.
A mixture of ternary intercalation compounds containing C ₆₄ Na (THF) and C ₇₂ Na (THF) as main components was obtained. after that,
The resulting mixture of ternary intercalation compounds was filtered and separated. Reference Example 2 1 g of finely chopped metallic sodium was added together with 4 g of benzophenone to 100 ml of tetrahydrofuran which had been sufficiently dehydrated with a molecular sieve, and the mixture was left standing at room temperature in the open air for 24 hours. then in the air
Add 5 g of Madagascar flaky graphite of 24 to 200 mesh (Tyler) having a broad peak in particle size distribution to 50 to 80 mesh (Tyler) dried at 110°C, and stir gently with the reaction vessel capped. , left standing at room temperature for 24 hours to form C ₃₂ Na(THF) ₃ ,
A mixture of ternary intercalation compounds containing C ₆₄ Na (THF) and C ₇₂ Na (THF) as main components was obtained. Thereafter, the resulting mixture of ternary intercalation compounds was filtered and separated. Reference Example 3 1 g of finely chopped sodium metal and 10 g of benzophenone were dried in air at 110°C to produce scaly graphite from Madagascar with a broad peak in particle size distribution of 24 to 200 mesh (Tyler) in the range of 50 to 80 mesh (Tyler). 5 g into 100 ml of tetrahydrofuran that had been sufficiently dehydrated with _CaH2 ,
After stirring gently with the reaction container capped, the mixture was allowed to stand at room temperature for 24 hours. Thus C ₃₂ Na (THF) ₃ , C ₆₄ Na
(THF), a mixture of ternary intercalation compounds containing C ₇₂ Na (THF) as the main components was obtained. The resulting mixture of ternary intercalation compounds was filtered and separated. Example 1 The ternary intercalation compound obtained in Reference Example 1 was placed in a quartz tube and placed in an electric furnace heated to 1000°C for 30 seconds at normal pressure to obtain expanded graphite that had expanded sufficiently. Table 1 shows the expansion coefficient of the obtained expanded graphite. Example 2 Expanded graphite was obtained in the same manner as in Example 1 except that the ternary intercalation compound obtained in Reference Example 2 was used. Table 1 shows the expansion coefficient of the obtained expanded graphite. Example 3 Expanded graphite was obtained in the same manner as in Example 1 except that the ternary intercalation compound obtained in Reference Example 3 was used. Table 1 shows the expansion coefficient of the obtained expanded graphite.

[Table] The above expansion coefficient is a value obtained by examining the thickness of raw graphite and expanded graphite in the C-axis direction using electron micrographs and using the following formula. Also, the expansion coefficients listed above are the average of 10 measurements for each sample. Expansion coefficient = Thickness of expanded graphite in C-axis direction / Thickness of raw graphite in C-axis direction

Claims (1)

[Scope of Claims] 1. A method for producing expanded graphite, which comprises heating and expanding a graphite ternary intercalation compound consisting of sodium, tetrahydrofuran, and graphite and/or its residual compound. 2. The graphite ternary intercalation compound is obtained by reacting sodium, tetrahydrofuran, and graphite in the presence of one selected from the group consisting of benzophenone and anthracene. The manufacturing method according to item 1.