JP3521224B2 - Method for producing porous carbon material from low molecular weight fluororesin and its use - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a low molecular weight fluororesin, a carbon precursor using the resin as a raw material and a method for producing a porous carbon material, and further, an electrical method using the porous carbon material. The present invention relates to a double layer capacitor.

[0002]

2. Description of the Related Art Conventionally, various porous carbon materials typified by activated carbon utilize their excellent characteristics of adsorption performance and separation function to remove impurities in gas or liquid, gas separation,
It has been widely used for solvent recovery. In recent years, these porous carbon materials are used for other purposes, such as a mass storage material for methane and hydrogen, which utilizes fine pores in the carbon material,
As an electronic device material having a function of filling and releasing a large amount of ions and electrolytes, its use as a negative electrode material of a secondary battery or an electric double layer capacitor material is rapidly expanding. A porous material having pores of a few nanometers (nm) or less is effective as a storage material for methane or hydrogen gas,
On the other hand, for electronic devices, a porous body having pores of several nm to several tens nm close to the size of ions or electrolytes or a solvated state of these is desirable.

Incidentally, conventional porous carbon materials are generally made of various organic wastes, coconut shells, coal, etc. as raw materials, and carbonized products obtained by heat-treating these are treated with steam, CO ₂ ,
It is manufactured by activating treatment with O ₂ or the like. However, the carbon materials produced by these activation methods have a wide distribution of pores of various sizes, from very small micropores to mesopores, to macropores in micron units.
It is insufficient to be used as a small-sized occlusion material capable of accommodating a large amount of gaseous substances or as a small-sized electronic device material having excellent characteristics. Especially when applied to electric double layer capacitor materials, when using commercially available activated carbon fiber, the electric capacity is about 140 F / g up to a specific surface area of 1000 m ² / g.
However, there is a problem that when the specific surface area is larger than that, it saturates and hardly increases. As described above, the carbon material has a large room for improvement in the control of the carbon structure that can effectively utilize the excellent characteristics of carbon, and in particular, the porous material having a uniform fine pore size suitable for the purpose of use. There is a demand for the development of carbonaceous materials.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned actual situation in the prior art. That is, an object of the present invention is to use a fluororesin as a starting material,
An object of the present invention is to provide a method for producing a porous carbon material having a large specific surface area and a high electric capacity because it has a large amount of fine pores having a uniform size in the mesopore region. Another object of the present invention is to provide an electric double layer capacitor having a large electric capacity per unit volume.

[0005]

The inventors of the present invention have already made a completely different raw material from the conventional one and, at the same time, used a completely different method for a carbon precursor before it became a carbon material. A method of manufacturing the carbon material prepared in 1. was proposed. That is, using a fluorine-based resin that has never been used as a raw material, the fluorine atoms contained in the resin are desorbed with an alkali metal, and then the by-produced alkali fluoride is removed to leave a carbonaceous substance remaining. Is used as a carbon precursor and heat-treated at a specific temperature to obtain a porous carbon material having a large number of uniform pore diameters. Subsequent to this, as a result of further intensive studies, the present inventors replaced the commercially available fluororesin used conventionally with low molecular weight fluorine obtained by treating the fluororesin with a special method. It was found that a resin raw material has a large amount of uniform pore diameters in the mesopore region, and a porous carbon material having a high specific surface area and a large electric capacity can be obtained, and the present invention has been completed. .

That is, the method for producing a low molecular weight fluororesin of the present invention is characterized in that a low molecular weight fluororesin obtained by depolymerizing the fluororesin is obtained by irradiating the fluororesin with gamma rays. Further, the method for producing a porous carbon material of the present invention is a method of reducing defluorination of a low molecular weight fluororesin obtained by depolymerization of a fluororesin by irradiating the fluororesin with gamma rays, with an alkali metal or an alkali metal-containing solution. The obtained reaction product is treated with an acid to remove the by-produced alkali metal fluoride, and the defluorinated carbonaceous material is used as a carbon precursor.

The method for producing a carbon precursor of the present invention is
The low molecular weight fluororesin obtained by depolymerizing the fluororesin by irradiating the fluororesin with gamma rays is subjected to reductive defluorination with an alkali metal or an alkali metal-containing solution, and the resulting defluorinated product and alkali metal fluoride It is characterized in that the coexisting reaction product is heat-treated in vacuum at 200 to 500 ° C. and then treated with an aqueous solution of hydrofluoric acid or hydrochloric acid to obtain a defluorinated carbonaceous substance as a carbon precursor. next,
The carbon precursor obtained by the above method was added in an inert atmosphere for 5
By high temperature heat treatment at a temperature of 00 to 3000 ° C.,
The method for producing a porous carbon material is characterized in that a porous carbon material having highly developed uniform pores in the mesopore region is obtained.

The electric double layer capacitor of the present invention is characterized in that the porous carbon material obtained by the above method is used for a polarizable electrode.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the present invention, a low molecular weight fluororesin is first produced by irradiating a fluororesin raw material with gamma rays to cleave the carbon chain in the fluororesin to an appropriate size, and then,
A porous carbon material is produced from the obtained low molecular weight fluororesin via a carbon precursor. The porous carbon material obtained in the present invention has a high specific surface area in which a large number of pores having a uniform pore size distribution in the mesopore region of 2 to 50 nm are formed, and has a large electric capacity. It is extremely useful as an electrode for capacitors and as a negative electrode carbon material for secondary batteries.

The method for producing a porous carbon material according to the present invention mainly comprises the following steps. (1) A low molecular weight fluororesin is produced by irradiating the fluororesin with gamma rays to depolymerize the fluororesin. (2) reacting the low molecular weight fluororesin obtained in (1) above with an alkali metal or an alkali metal-containing solution,
The fluorine atom in the fluororesin is desorbed with an alkali metal,
A reaction product containing a defluorinated product and an alkali metal fluorinated product is produced. (3) Next, the reaction product is treated with an acid to obtain a defluorinated carbonaceous material obtained by removing the by-produced alkali metal fluorinated product from the defluorinated product as a carbon precursor. At this time, it is preferable to heat-treat the reaction product in a temperature range of 200 to 500 ° C. in vacuum in a state where the defluorinated compound and the by-produced alkali metal fluorinated compound coexist before being acid-treated. (4) Further, a porous carbon material is produced from the carbon precursor. At that time, it is preferable to subject the carbon precursor to a high temperature heat treatment in an inert gas atmosphere in a temperature range of 500 to 3000 ° C., whereby a large number of pores having a uniform pore size in the meso region of 2 to 50 nm are distributed. A porous carbon material having a structure can be obtained.

Next, the above manufacturing process (1) in the present invention.
(4) will be described in order. First, the fluororesin used as the raw material in the first step is a fluororesin composed of carbon atoms and fluorine atoms, and the product name: polytetrafluoroethylene (PTF) commercially available as Teflon.
E), fluorinated ethylene propylene, a polymer composed of a carbon atom having an unsaturated carbon double bond and a fluorine atom, and the like. As the shape, it is preferable to use a powdery or thin film solid. As the gamma (γ) ray for irradiating the fluorine resin, any gamma ray that emits γ ray can be used, but ⁶⁰ Co is usually used. The irradiation treatment is performed in a vacuum or in an inert gas so that the irradiation amount is 1 to 100 so that the carbon chain can be cut into an appropriate size.
The irradiation treatment is performed for a time, preferably 8 to 80 hours. By this irradiation treatment, the fluororesin (melting point 332.0 ° C.)
As the irradiation time was increased to 8 hours, 40 hours, and 80 hours, the melting points of each were 325.6 ° C, 321.4 ° C,
A low molecular weight fluororesin having a temperature of 318.5 ° C. is obtained. FIG. 1 shows the measurement results of differential thermal analysis (DTA) and thermogravimetric analysis (TG) of a low molecular weight fluororesin obtained by subjecting the fluororesin to γ-ray irradiation treatment. The γ-ray irradiation dose (C / kg) in FIG. 1 is (a) none and (b) 3.12, respectively.
× 10 ³ , (c) 1.56 × 10 ⁴ , (d) 3.12
It is × 10 ⁴ .

Next, as the alkali metal used in the reductive defluorination reaction of the low molecular weight fluororesin in the second step, L
Although any metal element of i, Na, K, Cs, and Rb can be used, K is preferable from the viewpoint of handleability and the like. In addition, as its usage, those metal elements are used in a gas state at high temperature, or those metal ions and polycyclic aromatic ring compounds such as naphthalene and anthracene are dissolved in a solvent such as tetrahydroftane. Used as an alkali metal-containing solution (alkali metal anion radical solution).

As the defluorination reaction conditions in the present invention, it is preferable to gasify the alkali metal element under reduced pressure, particularly in a vacuum state to react with the low molecular weight fluororesin powder. The reaction temperature varies depending on the gasification temperature of the metal species used, but when metal potassium (K) is used, it is in the temperature range of 80 to 400 ° C., preferably about 200 ° C. . The reaction time depends on the shape of the low molecular weight fluororesin, but is about 2 to 12 hours in the case of powder. In this way, by performing the defluorination reaction of the low molecular weight fluororesin, the fluororesin is reduced and a large amount of carbon-
A reaction product in which a carbine-like substance (defluorinated product) of polyyne type having a carbon triple bond or a cumulene type having a cumulative double bond system of carbon and an alkali metal fluorinated by-product coexist is obtained. At that time, if K is used as the alkali metal, potassium fluoride (KF) is by-produced.

Next, in the third step, acid treatment of the above defluorinated compound is performed. By this acid treatment, a defluorinated carbonaceous substance, which is a residue obtained by removing an alkali metal fluorinated substance by-produced from the defluorinated substance, for example, KF, is obtained and used as a carbon precursor (precursor) of the porous carbon material. It is a thing. For the acid treatment, any acidic solution capable of removing the by-produced alkali metal fluoride from the defluorinated product can be used, but it is preferable to use a hydrofluoric acid aqueous solution (HF / H ₂ O) or a hydrochloric acid solution. .

In the third step, before the acid treatment with a hydrofluoric acid aqueous solution or the like, in the coexistence of the carbine-like substance and the alkali metal fluoride, the temperature is in the range of 200 to 500 ° C. in vacuum for 30 minutes to 5 hours. It is preferable to perform heat treatment for about 1 to 2 hours. By carrying out this heat treatment, aggregated clusters of alkali metal fluorinated compounds present in the defluorinated carbine-like substance are formed, and when the heat treatment temperature is variously changed, the size of the formed clusters becomes different. I knew it would come.
Therefore, in the third step, the heat treatment described above is performed under appropriate conditions to adjust the size of clusters to be formed, and then the clusters are treated with an aqueous solution of hydrofluoric acid or a hydrochloric acid solution to remove the clusters. With a nano-sized diameter in the mesopore region of ~ 50 nm, it has a large number of arbitrary uniform pore diameters,
A defluorinated carbonaceous material having a carbocyclic structure can be appropriately produced. The defluorinated carbonaceous material thus obtained is preferably used as the carbon precursor of the porous carbon material.

Next, in the third step, using the above-mentioned carbon precursor, a porous carbon material can be easily manufactured by a general method for carbon materials. However, the carbon precursor is a defluorinated carbonaceous material having a 6-membered carbon ring structure in which a large number of pores are formed by removing clusters and a large number of carbon-carbon triple bonds are cyclized. Therefore, in an atmosphere of an inert gas such as argon or neon, the temperature is in the range of 500 to 3000 ° C., preferably about 80.
A high temperature heat treatment at 0 ° C. makes it possible to produce a porous carbon material having a large number of pores precisely controlled to have a uniform pore diameter in the mesopore region.

Generally, the lower the molecular weight fluororesin obtained by increasing the irradiation amount of γ-rays to the fluororesin, the more the pores in the mesopore region of the obtained porous carbon material increase and the larger the specific surface area of The electric capacity increases to about 240F / g
It was confirmed that Therefore, the porous carbon material obtained by the production method of the present invention has a large number of uniform pores in the mesopore region of 2 to 50 nm and has a large specific surface area. By using it as an electrode, the electric capacity can be increased.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 Commercially available polytetrafluoroethylene (PTFE) powder (trade name: Teflon, average particle size: 20 μm) was irradiated with gamma rays in a vacuum for 8 hours (irradiation amount: 3.12 × 10 ³ C).
/ Kg) to obtain a depolymerized low molecular weight fluororesin. The melting point of the obtained low molecular weight fluororesin was 325.6 ° C. according to thermogravimetric analysis [see (b) in FIG. 1]. This gamma-ray treated PTFE powder and potassium metal,
Each was held in vacuum separately. These were placed in a constant temperature bath of 200 ° C., and the PTFE powder was exposed to potassium vapor to gradually progress the defluorination reaction. The white PTFE powder gradually changed to black as the reaction proceeded, but it was left in a constant temperature bath until the reaction of all the powders was completed to obtain a black powder. Then, the generated black powder is heat-treated at 200 ° C. for 1 hour while being degassed in vacuum as it is, and then the black powder after the heat treatment is taken out in air and added to the hydrofluoric acid solution for 24 hours. After stirring, it was filtered and separated using a propylene (PP) or glass filter, washed with distilled water, and dried to obtain a defluorinated carbonaceous material (carbon precursor). Next, this carbon precursor was heat-treated in argon gas at a temperature of about 800 ° C. to obtain a porous carbon material.

Example 2 Commercially available polytetrafluoroethylene (PTFE) powder (trade name: Teflon, average particle size: 20 μm) was irradiated with gamma rays in a vacuum for 40 hours (irradiation amount 1.56 × 10 ^4).
C / kg) to obtain a depolymerized low molecular weight fluororesin. The melting point of the obtained low molecular weight fluororesin is 321.4.
It was ℃ [see (c) in FIG. 1]. A porous carbon material was obtained in the same manner as in Example 1 except that the obtained low molecular weight fluororesin was used.

The porous carbon materials obtained in Examples 1 and 2 were subjected to adsorption measurement with nitrogen gas of 77 K to determine the pore distribution. FIG. 2 shows adsorption / desorption isotherms (nitrogen gas at 77K) of the porous carbon material obtained from the fluororesin. In FIG. 2, (a) shows the case where γ-ray irradiation was not performed, and (b) shows the γ-ray irradiation amount of 3.12 × 10 ³ C
/ Kg, (c) shows a γ-ray irradiation amount of 1.56
It shows the one treated with × 10 ⁴ C / kg. As shown in FIG. 2, the adsorption / desorption isotherm showed that the adsorption amount increased as the γ-ray irradiation amount increased.

Table 1 below shows the specific surface area and the electric capacity of the porous carbon material obtained from the fluororesin. When the low molecular weight fluororesin obtained in Example 2, that is, the fluororesin irradiated with γ rays having an irradiation dose of 1.56 × 10 ⁴ C / kg was used, the obtained porous carbon material was The specific surface area was as high as about 1560 m ² / g as seen in Table 1. Further, the mesopores (pore diameter 2 to 50 nm) have a γ
It was found that it developed with an increase in the radiation dose.

[0022]

[Table 1]

Further, FIG. 3 shows the pore distribution of the porous carbon material calculated from the desorption curve. As shown in FIG. 3, the porous carbon materials (b) and (c) obtained by the present invention.
The average pore diameter of No. 2 had a sharp peak of pore diameter distribution at about 4 nm, and the pore volume was extremely large. Further, as for the relationship between the electric capacity of the porous carbon material and the specific surface area, as shown in FIG. 4, the electric capacities of the porous carbon materials (b) and (c) obtained by the present invention are the same as those of the conventional activated carbon. Compared to that of fiber, it is significantly higher for the same specific surface area,
It was also found that the amount was significantly higher than that of the case (a) which was not irradiated with γ-rays.

[0024]

INDUSTRIAL APPLICABILITY According to the present invention, a low molecular weight fluororesin suitable as a raw material for a porous carbon material useful as an electric material or a gas storage material can be easily produced by a simple treatment of the fluororesin. Porous carbon material obtained by the production method of the present invention, in the pore size of the mesopore range, since it is an excellent porous carbon material having a large amount of desired pores uniformly controlled, various gas storage material, For example, storage materials such as lower hydrocarbons such as hydrogen and methane, electrode materials for secondary batteries,
It is extremely useful in a wide range of fields such as electric double layer capacitor materials.

[Brief description of drawings]

FIG. 1 is a graph showing analytical data of low molecular weight fluororesin obtained by γ-ray irradiation treatment of fluororesin.

FIG. 2 is a graph of adsorption / desorption isotherms (nitrogen gas at 77K) of a porous carbon material obtained from a fluororesin.

FIG. 3 is a graph showing a pore distribution of a porous carbon material calculated from a desorption curve.

FIG. 4 is a graph showing the relationship between the electric capacity and the specific surface area of a porous carbon material.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H01G 9/058 H01M 4/58 H01M 4/58 C08L 27:12 // C08L 27:12 H01G 9/00 301A

Claims (4)

(57) [Claims] 1. A low molecular weight fluororesin obtained by depolymerizing a fluororesin by irradiating the fluororesin with gamma rays,
The defluorinated carbonaceous material obtained by reducing and defluorinating with an alkali metal or a solution containing an alkali metal and treating the resulting reaction product with an acid to remove the by-produced alkali metal fluoride was used as a carbon precursor. A method for producing a porous carbon material having the characteristics. 2. A low molecular weight fluororesin obtained by depolymerizing a fluororesin by irradiating the fluororesin with gamma rays,
Reductively defluorinate with an alkali metal or an alkali metal-containing solution, and heat the reaction product of coexistence of the obtained defluorinated product and alkali metal fluoride at 200 to 500 ° C. in vacuum, and then treat with a hydrofluoric acid or hydrochloric acid aqueous solution. A method for producing a carbon precursor, which comprises using the defluorinated carbonaceous material obtained by the above as a carbon precursor. 3. The carbon precursor obtained by the method according to claim 2 is subjected to a high temperature heat treatment at a temperature of 500 to 3000 ° C. in an inert atmosphere to highly develop uniform pores in the mesopore region. A method for producing a porous carbon material, which comprises obtaining a porous carbon material. 4. An electric double layer capacitor, wherein the porous carbon material obtained in claim 1 or 3 is used for a polarizable electrode.