JPH11157820A - Expanded graphite, its production and oil absorbing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oil absorbing material attained in excellent forming workability and having excellent oil absorbing ability by oxidizing a carbon fiber formed material with an acid and an oxidizing agent and after that, heating. SOLUTION: A method for producing an expanded graphite from the carbon filter formed material is constituted of a process for producing a graphite intercalation compound by oxidation reaction and a process for expanding by heating. The carbon fiber formed material means a formed material using a carbon fiber (e.g. ccbon fiber woven fabric, carbon fiber felt, carbon fiber mat or the like). As the oxidizing method of the carbon fiber formed material, a chemical dipping process, electrolytic oxidation process and the like may be cited, but the chemical dipping method is preferable in the view point of productivity and cost. The method uses a mixture of a concentrated acid with a strong oxidizing agent. As the oxidizing agent, nitric acid, hydrogen peroxide, potassium dichromate, peroxo ammonium disulfate and the like are exemplified. The expanded graphite is obtained by heating the graphite intercalation compound after being oxidized at 500-3,000 deg.C under atmospheric pressure or reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to expanded graphite, a method for producing the same, and use thereof.

[0002]

2. Description of the Related Art Conventionally, expanded graphite using a natural graphite material as a starting material has been known, but there is a problem that this expanded graphite is difficult to process. Japanese Patent Application Laid-Open No. Hei 5-96157 proposes a molding method in which expanded graphite is compression-molded and a binder is added, but there is a problem that the method of adding a binder is troublesome.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel expanded graphite excellent in moldability, a method for producing the same, and an oil absorbent having excellent oil absorbing ability. The present inventors, in the production of carbon fibers, especially pitch-based carbon fibers,
Focusing on the fact that by selecting the raw material pitch and production conditions, it is possible to produce a carbon fiber having an extremely high elastic modulus with a developed graphite structure at low cost, and as a result of further investigation, the present invention has achieved remarkable effects did.

[0004]

The present invention firstly relates to expanded graphite obtained from a carbon fiber molded article. Secondly, the present invention is a method for producing expanded graphite, which comprises treating a carbon fiber molded article with an acid and an oxidizing agent. Thirdly, the present invention is an oil absorbent comprising expanded graphite obtained from a carbon fiber molded product.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a carbon fiber molded product means a carbon fiber alone or a molded product using carbon fiber. In the present invention, the carbon fiber refers to a carbon fiber precursor of 80%.
Fibers fired at a temperature exceeding 0 ° C., preferably at a temperature of 1000 ° C. or more. In particular, 2000 ° C. or higher, more preferably 2600 ° C. or higher, further preferably 2900 to 32
So-called graphitized fibers treated at a high temperature of 00 ° C are preferred carbon fibers. As the carbon fibers used in the present invention, pitch-based carbon fibers, polyacrylonitrile-based carbon fibers, carbon fibers such as rayon-based carbon fibers can be used, but the pitch-based carbon fibers are preferable because the graphite structure easily develops during firing. . As a raw material of the pitch-based carbon fiber, a petroleum-based pitch, a coal-based pitch, and a synthetic-based pitch are preferably used. Specific examples of petroleum pitch include decant oil pitch and ethylene tar pitch, and specific examples of coal pitch include coal tar pitch and coal liquefied pitch. Specific examples of the synthetic pitch include various pitches such as a naphthalene pitch.

In the present invention, among the above-mentioned pitches, a pitch containing an optically anisotropic phase, that is, a mesophase pitch is preferably used.
A pitch of -100%, preferably 80-100%, more preferably 90-100% is used. In the present invention, the mesophase pitch is a pitch indicating an optically anisotropic phase that can be seen when observing a cross section of the pitch with a polarizing microscope, and the content is indicated by an area fraction of the optical anisotropy. . The pitch is spun by a usual melt spinning method. As the spinning mode, the melted mesophase pitch is spun by passing through a nozzle hole, and various methods can be selected depending on the difference in the take-up method. Specifically, there are a method of obtaining continuous long fibers, a method of cutting pitch fibers immediately after spinning to obtain chopped fibers, and a method of obtaining short pitch fibers by introducing gas into a nozzle (so-called melt blow method). Either spinning method can be used.

The yarn diameter of the pitch fibers is usually 7 to 50 μm, preferably 7 to 20 μm. The obtained pitch fiber is collected on a can or a conveyor, and subsequently subjected to a firing treatment. The spinning viscosity is desirably as low as possible from the viewpoint of promoting the development of the graphite structure during firing, and more specifically, the spinning is performed at a viscosity of 60 Pa · s or less, preferably 10 to 30 Pa · s. The obtained pitch fiber is usually in an oxidizing gas atmosphere at 100 to 360 ° C, preferably 130 to 360 ° C.
The infusibilization treatment can be carried out at a temperature of 320 ° C. for usually 10 minutes to 10 hours, preferably 1 to 6 hours. As the oxidizing gas, oxygen, air, ozone, or a mixture thereof with nitrogen dioxide, chlorine, or the like is used.

[0008] The infusibilized fiber is heated to 2600 ° C or higher, preferably 29 ° C, in an atmosphere of an inert gas such as nitrogen or argon.
By performing the graphitization treatment at a temperature of 00 ° C to 3200 ° C,
A carbon fiber can be obtained. In addition, a primary carbonization treatment may be performed at 300 to 800 ° C. in an inert gas atmosphere before the firing treatment.

As a method for producing chopped carbon fiber, in addition to the above-described method of cutting immediately after spinning, a method of cutting after primary carbonization or graphitization can also be adopted.
In the present invention, expanded graphite is produced from a carbon fiber molded article, and the production method comprises a process of producing a graphite intercalation compound by an oxidation reaction and a process of expanding by heating.

A carbon fiber molded article is used as a starting material for the oxidation reaction. A carbon fiber molded product refers to a molded product using carbon fiber alone or carbon fiber, for example, carbon fiber fabric, carbon fiber felt, carbon fiber mat, chopped carbon fiber, carbon fiber two-dimensional fabric, carbon fiber three-dimensional fabric. Alternatively, a carbon fiber unidirectional material may be used, and a prepreg obtained by further impregnating a resin into these carbon fiber molded articles, or after adding a binder such as pitch, resin, graphite powder or the like to these carbon fiber molded articles, may or may not be added. It also includes, if necessary, carbonized and fired carbonized materials, and also includes so-called carbon fiber reinforced carbon composite materials using a matrix of pitch, resin carbide, pyrolytic carbon, and the like.
As the carbon fiber used for the carbon fiber molded article, either a continuous long fiber or a short fiber can be used. The carbon fiber molded article may be a blended fiber, a blended fiber or a blended fabric of carbon fibers and organic fibers, and the organic fibers can be substantially eliminated by firing or chemical treatment. As the organic fibers, natural fibers and synthetic fibers can be used, and specifically, cotton yarn, silk yarn, nylon fiber, Kevlar fiber, rayon fiber and the like can be used.

As the oxidizing method, a known method such as a chemical immersion method or an electrolytic oxidation method can be used, and the chemical immersion method is preferable in terms of productivity and cost. In the chemical immersion method, a mixture of a concentrated acid and a strong oxidizing agent is usually used, but after adding an acid to a raw material such as a carbon fiber molded product, the oxidizing agent can be added. The oxidizing agent can be added simultaneously or a mixture of acid and oxidizing agent. Organic acids, inorganic acids, and mixtures thereof can be used as the acid. Sulfuric acid, fuming sulfuric acid, fuming nitric acid, phosphoric acid and the like are used as the inorganic acid, and acetic acid and the like are used as the organic acid. Sulfuric acid is most preferred. The concentration of the acid can be usually 50 to 100%, preferably 90 to 100%.

The oxidizing agent includes nitric acid, nitrate, hydrogen peroxide, potassium chromate, potassium dichromate, potassium chlorate, ammonium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, perchloric acid, Chlorate can be used. The oxidizing agent can be used by dissolving it in a solution such as water. In this case, the concentration of the oxidizing agent is usually 1 to 100%, preferably 20 to 90%. The proportions of the acid and the oxidizing agent are usually 1 to 100 parts by weight of the acid and 0.3 to 100 parts by weight of the oxidizing agent per 1 part by weight of the carbon fiber molded article. The graphite intercalation compound after the oxidation treatment can be washed with water or water to which an organic acid or an organic acid ester is added to remove the acid adhering to the graphite surface, and then dehydrated and dried. As the organic acid or organic acid ester, formic acid, acetic acid, oxalic acid or an alkyl ester thereof can be used. The graphite intercalation compound after the oxidation treatment can be washed with water if necessary, and dried.However, the graphite intercalation compound is further treated with an alkaline solution such as ammonia, sodium hydroxide, or potassium hydroxide, an alkaline gas, or the like. If necessary, it can be further washed with water or the like.

[0013] The graphite intercalation compound after the oxidation treatment is at 500 ° C to 3000 ° C, preferably at 80 ° C under atmospheric pressure or reduced pressure.
By heating at 0 ° C. to 2000 ° C., expanded graphite can be obtained. The expanded graphite obtained by the present invention is suitable as it is, or after a simple processing, as a conventional expanded graphite, as a raw material of a material used in various industrial fields, or as an oil absorbing material. Can be used. For example, the oil absorbent using the expanded graphite of the present invention can efficiently recover oil in a crude oil spill accident and remove oil in waste water. Expanded graphite used as an oil absorbing material can be easily regenerated by a chemical method such as heat treatment or a mechanical method such as squeezing,
At this time, the oil recovered at the same time can be reused.

[0014]

As described above, expanded graphite can be easily obtained by using a carbon fiber molded article as a raw material, and the expanded graphite can be used as an excellent oil absorbing material.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. (Example) Synthetic carbon fiber spinning pitch was adjusted to a spinning viscosity of 3.
Melt-spinning at 0 Pa · S, spun pitch fiber 10 m
It was cut to m length and collected in a can. The obtained pitch fiber diameter was 12.5 μm. While accommodating the pitch fibers in cans, 2 ° C. in air containing 1% NO ₂ /
The temperature was raised to 240 ° C. in min and maintained for 60 minutes to obtain infusible fibers. Next, the infusibilized fiber was heated to 700 ° C. at a rate of 10 ° C./min as it was in a nitrogen gas atmosphere, and kept for 15 minutes to perform temporary carbonization.
Graphitization was performed at a temperature of 5 ° C. for 5 minutes to obtain carbon fibers. 98%
After sulfuric acid and the carbon fiber are mixed and stirred, 30% hydrogen peroxide solution is added thereto and reacted for 12 hours. Then, the treated carbon fiber is sufficiently washed with water, dried, and heated to 800 ° C. It was placed in a furnace and subjected to a heat treatment to obtain expanded graphite.
When water and Fuel Oil A were added to a beaker and expanded graphite was added, the heavy oil was absorbed by the expanded graphite and the heavy oil layer in the beaker disappeared. After suction filtration using filter paper, the filtrate was colorless and did not contain oil. The weight measurement of the expanded graphite showed that 55 g of heavy oil was absorbed per 1 g of carbon fiber. The carbonized yarn obtained by subjecting the carbonized yarn to graphitization treatment at 2500 ° C. as a starting material was subjected to expansion treatment in the same manner as described above. The expansion was not sufficient probably because the degree of graphitization was insufficient, and the absorption amount of heavy oil was smaller than the above.

Continuation of the front page (72) Inventor Michio Inagaki Hokkaido University Graduate School of Engineering, Hokkaido, Hokkaido

Claims (3)

[Claims] 1. An expanded graphite obtained from a carbon fiber molded article. 2. A method for producing expanded graphite, comprising treating a carbon fiber molded article with an acid and an oxidizing agent. 3. An oil absorbent comprising expanded graphite obtained from a carbon fiber molded product.