JPH01115882A - Production of porous carbonaceous material - Google Patents

Abstract

PURPOSE:To obtain a porous carbonaceous material having a sharp distribution of pore diameter and excellent air permeability, strength, etc., by blending mesophase microspheres (powder) with a pore forming agent and thermosetting resin, forming the resultant blend and calcining the formed blend in a nonoxidizing atmosphere. CONSTITUTION:(A) Mesophase microspheres or powder is blended with (B) a pore forming agent (e.g. ammonium chloride) and (C) a thermosetting resin (e.g. phenolic resin) and the resultant blend is then formed and calcined in a nonoxidizing atmosphere to afford the aimed porous carbonaceous material. The obtained carbonaceous material is preferably used as electrode substrates for phosphoric acid type fuel cells, etc. Furthermore, the component (A) is obtained by heat-treating heavy oil, pitch, etc., at about 350-500 deg.C temperature, forming spherulites consisting of optically anisotropic spheres in a pitch mother phase and collecting the spheres, etc.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a porous carbon material.

More specifically, the present invention relates to a method for producing a porous carbon material having a sharp pore size distribution, excellent air permeability, electrical conductivity, and thermal conductivity, and having high mechanical strength and suitable as an electrode substrate for fuel cells.

[Conventional technology]

In recent years, porous carbon materials have attracted attention as filter materials for processing molten aluminum, filtering impurities in chemical solutions, filtering boiler condensate, and as electrode substrates for fuel cells. In particular, in fuel cells, a large number of cells with an electrolyte sandwiched between electrodes are assembled via separators, so not only are separators and electrodes required to be thin materials, but also have sufficient dimensional accuracy such as sufficient flatness and smoothness. , materials with excellent low thermal expansion coefficient, heat resistance, chemical resistance, etc. are required. In particular, in addition to the above characteristics, the electrode substrate is made of a material with good gas permeability, that is,
Porous materials with high air permeability and a sharp pore size distribution are desired.

Such porous carbon materials as electrode substrates for fuel cells have conventionally been manufactured by the method described below.

The first method involves mixing carbon fibers, a binder, and an organic particulate material, press-molding the resulting mixture, and firing it at 1000 to 3000°C in an active atmosphere after post-curing (Japanese Unexamined Patent Publication No. 59/1993). -141170).

The second method is to apply a resin treatment to a carbon fiber cloak to make it into a prepreg, heat and pressurize the prepreg carbon fiber cloak to harden it, and then carbonize it (Japanese Patent Application Laid-open No. 57429814), or carbonize it to carbon fiber paper. This is a method (Japanese Patent Publication No. 53-43920) in which resin is impregnated, then carbonized, and vapor phase pyrolytic carbon is further deposited.

[Problem that the invention seeks to solve]

However, although these methods can produce products with excellent electrical and thermal conductivity because they contain carbon fibers, the carbon fibers and matrix (binder, resin, carbonized The problem was that the difference in shrinkage rate of the polyester resins could easily lead to cracks. In other words, while the matrix shrinks significantly during the carbonization process, the carbon fibers do not shrink at all, resulting in cracks (
It was difficult to sharply control the pore size distribution. The lack of a sharp pore size distribution is a fatal defect, especially in applications such as fuel cell electrode substrates.

Therefore, the object of the present invention is to have a sharp pore size distribution,
Another object of the present invention is to provide a carbon material with excellent specifications such as air permeability, electrical conductivity, thermal conductivity, and mechanical strength.

[Means for solving problems]

The means for solving the above problems and achieving the object of the present invention is to mix and mold mesophase small spheres or mesophase powder, a pore-forming agent, and a thermosetting resin, and then mold the molded product under a non-oxidizing atmosphere. It is characterized by being fired in

[For production]

The present invention is characterized in that mesophase spherules or mesophase powder (the present invention includes the inclusion of both) instead of the carbon fibers used in the conventional method. Since the mesophase spherules or mesophase powder are easily graphitized substances, they easily become graphite crystals by carbonization firing, and a product with excellent electrical conductivity and thermal conductivity can be obtained. In addition, since the mesophase spherules or mesophase powder have the property of shrinking significantly during the carbonization process, like the thermosetting resin, after carbonization, the charcoal derived from the mesophase spherules or mesophase powder and the carbide derived from the thermosetting resin are combined. It is possible to prevent the occurrence of cracks due to the difference in shrinkage rate at the interface between the Therefore, since pores are formed according to the particle size and amount of the pore-forming agent, it is easy to control the pore size and porosity of the product, and the pore size distribution can be made sharp. can.

Incidentally, by performing the carbonization firing of the molded product in a non-oxidizing atmosphere, firing of the carbide can be prevented and the desired carbon material can be obtained.

[Specific structure of the invention]

The present invention will be explained in more detail below.

The thermosetting resin in the present invention is a resin that can give a carbide by carbonization firing, for example,
Examples include phenol resins, furan resins, xylene resins, epoxy resins, etc., but phenol resins and furan resins with high carbonization yields are preferred, and those with carbonization yields of 50 or more heavy walls are preferred if possible.

Next, the mesophase spherules or mesophase powder may be produced from any petroleum-based or coal-based pitch. However, carbon materials with few impurities are required from the viewpoint of phosphoric acid corrosion resistance and stability of battery reactions, so in the case of coal-based materials, it is recommended that the raw materials for producing mesophase spherules or mesophase powder be purified. is preferred. As a raw material refining method, for example, as shown in Japanese Patent Publication No. 5B-22070, a method is preferred in which a ketone solvent is mixed with coal-based heavy oil from which fractions with a boiling point of 270°C or less have been removed at room temperature and pressure. used.

Next, the mesophase small spheres and mesophase powder used in the present invention refer to the following. Normally, when petroleum-based or coal-based heavy oil or pitch is heat-treated at 350 to 500°C, optically anisotropic spheres called spherulites are formed in the pitch matrix in the early stage of the heat treatment, and As the heat treatment continues, the crystals coalesce and grow repeatedly, and the entire pitch becomes an optically anisotropic material, the so-called bulk mesophase. The above spherulites and bulk mesophases differ depending on the heat treatment conditions, but in terms of -a, they do not show a softening point, that is, they have coke-like properties of infusibility, but on the other hand, they contain several percent by weight of volatile matter. It is a carbon precursor that also has several properties. The mesophase microspheres as used in the present invention are the above-mentioned spherulites, and the mesophase powder is obtained by pulverizing the above-mentioned bulk mesophase.

This mesophase small sphere or mesophase powder has a carbon content of 92% or more, a volatile content of 7 to 13% by weight up to 900°C, a linear shrinkage rate of 1% or more when heated to 500°C, and an average Preferably, the particle size is 40 μm or less. The reason for this is as follows. In other words, when the carbon content is less than 92%, elements other than carbon decompose and gasify during the firing process, resulting in increased weight loss, and atoms other than carbon inhibit graphitization, resulting in poor thermal conductivity and There is a possibility that electrical conductivity and phosphoric acid resistance will not improve.

In addition, if the volatile content up to 900°C is less than 7% by weight,
During the firing process, the wettability with the thermosetting resin is poor, and cracks occur at the interface with the mesophase spherules or mesophase powder, making it difficult to control the pore size distribution. On the other hand, 13% by weight
If it exceeds this value, a large amount of volatile matter generated from inside the mesophase small spheres or mesophase powder may result in a foam or porous body, which may also make it difficult to control the pore size distribution. Furthermore, "linear shrinkage rate when heated to 500°C" is measured by pressure-molding mesophase small spheres or mesophase powder alone at a pressure of 2t/cd or more and taking a sample from the resulting compact. This is the value. If this linear shrinkage rate is less than 1%, gaps will occur at the interface between the carbon particles derived from the mesophase small spheres or mesophase powder after carbonization firing and the carbon particles derived from the thermosetting resin, and the pore size distribution will expand. This is not preferable because it makes it difficult to use.

The pore-forming agent used in the present invention is preferably a substance that does not flow, decompose, or sublimate below the curing temperature of the thermosetting resin. The reason for this is that until the thermosetting resin is cured, the spaces corresponding to the desired pore size and porosity are filled with the pore-forming agent, and it is not until the next carbonization process that the pore-forming agent decomposes or sublimates. This is to generate the desired pore size and porosity. Pore-forming agents having such characteristics include ammonium salts such as ammonium iodide, ammonium chloride, ammonium hydrogen sulfate, and hydroxyammonium sulfate; hexamethylenetetramine; cured products of epoxy resin (epoxy resin liquid
Organic substances such as those cured by heat treatment at ℃) can be used.

Next, a method for manufacturing a carbon material according to the present invention will be explained. First, mesophase small spheres or mesophase powder 2~
25% by weight, 10-30% by weight of thermosetting resin, and 50-85% by weight of pore former. When the blending ratio of mesophase small spheres or mesophase powder is less than 2% by weight, the effect of blending the mesophase small spheres or mesophase powder cannot be obtained, and the thermal conductivity and electrical conductivity decrease. On the other hand, 2
Even though the surface area of mesophase spherules or mesophase powder increases when more than 5% by weight is added,
Since the proportion of the thermosetting resin blended is relatively reduced, the mesophase small spheres or mesophase powder, and the pore forming agent cannot be uniformly bound by the thermosetting resin, resulting in a decrease in strength. Note that carbon fiber may be added as a reinforcing material in a range of 1 to 3% by weight. In this case, although cracks occur at the interface between the carbon fiber and the thermosetting resin, since the blending ratio of carbon fiber is small, the pore distribution of the carbon material is not substantially expanded, and therefore the gist of the present invention is not achieved. It's not something to deviate from. The carbon fibers are preferably in the form of short fibers with a length of about 0.5 to 10 meters or paper-like fibers made from short fibers with a length of about 0.5 to 10 meters.

Next, the mixture obtained in this way is charged into a mold,
Normally 5-150kr/cd at a temperature of 130-200℃
Heat and press mold at a pressure of Next, this molded body is heated at 130 to 200° C. for 10 to 30 hours to post-cure, if necessary. The post-cured compact is carbonized and fired at a heating rate of 0.5 to at least 800°C in a non-oxidizing atmosphere, such as Nt gas or gauge gas, and is further graphitized if necessary to form porous carbon. It is considered as a material.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

(Example 1) Carbon content 93.3% by weight, volatile content up to 900°C 10
．． Mesophase microspheres with a linear shrinkage rate of 3% up to 500°C and an average particle size of 15 μl, and a phenol/novolac resin powder (rPGA 4504) with a carbonization yield of 52% by weight at 1000°C, manufactured by Gunei Chemical Co., Ltd. ■) and N crushed so that 70% by weight or more has a particle size of 10 to 50μ
H4 (l) powder was mixed in the proportions shown in Table 1.

Next, this mixture was charged into a mold having a planar area of 1 m x 1 m, and heated and pressure molded at a temperature of 180°C and a pressure of 80 kg/aJ for 30 minutes to obtain a molded product with a thickness of 0.5 m, and this molded product was molded for 20 hours. After increasing the temperature to 200℃,
It was held for 20 hours for post-curing.

Next, the post-cured compact was carbonized by heating to 1000°C at a rate of 4°C/Hr under N2 gas flow in a container filled with coke powder, and then carbonized at a rate of 4°C/ll in an argon atmosphere.
The temperature was raised to 2500° C. at a rate of 1 n to obtain a graphitized material with a thickness of 0.4 m. The physical properties of this graphitized product were measured, and the results shown in Table 1 were obtained. Note that the air permeability in Table 1 is based on a differential pressure of 1 k
This is the measured value of the amount of N gas passing through in g/aJ at room temperature.

Further, "pore radius of 70% or more" in Table 1 is a value determined from the pore distribution measured by mercury porosimetry using a mercury porosimeter. Since the narrower the pore radius range, the sharper the pore size distribution, "a pore radius of 70% or more" was used as a measure of the spread of the pore distribution.

(Example 2) Carbon content 92.8% by weight, volatile content up to 900°C 12
．． 0% by weight, a linear shrinkage rate of 5% up to 500°C and an average particle size of 15 μm was used instead of the mesophase spherules, and 70% by weight or more had a particle size of 5 to 30%.
NH4Cj crushed to μm! A graphitized product was obtained in exactly the same manner as in Example 1, except that Graphite was used. The results are shown in Table 1. Further, FIG. 1 shows the pore distribution measurement results of G as an example of the measurement of pore size distribution.

(Example 3) Of the blending ratio of mesophase powder in Example 2, only 3% by weight was mixed with a diameter of 18 μm, a length of 0.7 μm, and a tensile strength of 60 kgr.
A graphitized product was obtained in exactly the same manner as in Example 1 except that carbon fibers with a diameter of 1 m" were used. The results are shown in Table 1.

(Example 4) Furan resin was used instead of the phenol resin in Example 1, and (NH4)HSO4 was used instead of NH4Cj2.
A graphitized product was obtained in exactly the same manner as in Example 1, except that .

The results are shown in Table 1.

(Comparative Example 1) A graphitized material was obtained in exactly the same manner as in Example 1, except that the same carbon fiber as used in Example 3 was used instead of the mesophase powder of Example 1. The results are also shown in Table 1. Also,
FIG. 2 shows the results of measuring the pore distribution of T.

〔Effect of the invention〕

As described above, according to the present invention, a porous carbon material having a sharp pore size distribution, excellent air permeability and strength, and extremely suitable as an electrode substrate for a phosphoric acid fuel cell can be provided.

[Brief explanation of the drawing]

Figure 1 shows the pore distribution of Example 2-G, Figure 2 shows Comparative Example 1.
- It is a figure which shows the pore distribution of T. Q2- History ≠ ≠ ≠ 1 1 4 1 3 3 3 3 3 4 3 4 3 4 4 4 4 274421 No. 2, Name of the invention Method for manufacturing porous carbon material 3, Relationship with the person making the amendment Patent applicant address name (211) Sumitomo Metal Industries, Ltd. 4, Agent ■
101 Name (8264) Patent attorney Yoshihisa Nagai 5
, Date of amendment order Voluntary amendment 6, Specification to be amended, Detailed explanation of the invention column 7, Contents of amendment (1) The description and Detailed explanation of the invention column are corrected as follows. ■Page 5, line 5, ``Burning of carbide'' was changed to ``Combustion of carbide by oxidation.'' ■Page 6, line 12, “crystal” is replaced with “spherulite”. ■Page 11, line 19, "of Nz gas with a differential pressure of 1 kg/ctA" is changed to "of air with a differential pressure of 0.013 kg/-". ■Follow-11

Claims (1)

[Claims] (1) A method for producing a porous carbon material, which comprises mixing and molding mesophase small spheres or mesophase powder, a pore-forming agent, and a thermosetting resin, and then firing the molded product in a non-oxidizing atmosphere. .