JP2015172161A - porous carbon sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous carbon sheet capable of improving corrosion resistance and improving heat resistance.SOLUTION: The porous carbon sheet comprises: a porous carbon powder which has mesopores and in which the mesopores are irregularly arranged in a carbonaceous wall, and adjacent mesopores communicate with each other; and a binder. It is preferable that the ratio of the binder to the porous carbon powder is 5 to 50 wt.% inclusive. It is also preferable that the porous carbon sheet has a film thickness of 250 to 1,000 μm inclusive.

Description

  The present invention relates to a porous carbon sheet.

  Sheets used for gas filters, gas diffusion layers, spacers, catalyst carriers, electrodes, condensers, and the like are made of various materials such as metals and ceramics. When used in such applications, heat resistance may be required or corrosion resistance (oxidation resistance) may be required depending on the place of use.

  As an example in which the sheet is used, a proposal has been made to stack a plurality of metal sheets to form a condenser (Patent Document 1 below).

JP2013-86060A

  However, since the sheet shown in Patent Document 1 is made of metal, there is a problem that it may corrode when used under severe conditions such as high temperature and high humidity.

  Then, this invention aims at providing the porous carbon sheet which can improve heat resistance while improving corrosion resistance.

  In order to achieve the above object, the present invention is characterized by comprising a porous carbon powder having mesopores, in which adjacent mesopores communicate with each other, and a binder.

  According to the present invention, there is an excellent effect that the corrosion resistance can be improved and the heat resistance can be improved.

It is a figure which shows the manufacturing process of the porous carbon used for this invention, Comprising: The figure (a) is explanatory drawing which shows the state which mixed the polyamic acid resin and magnesium oxide, The figure (b) is the state which heat-processed the mixture FIG. 3C is an explanatory view showing porous carbon. It is a graph which shows the result of the thermogravimetric analysis in air atmosphere in sheet | seat A1, A2, Z and porous carbon. In sheet A1, A2, Z, is circulated alternately and dry N ₂ and a wet N _2, is an illustration of an apparatus for measuring the weight change of each sheet. It is a graph which shows the responsiveness to atmospheric humidity in sheet | seat A1. 5 is a graph showing the response to atmospheric humidity in a sheet Z. It is a photograph which shows the state of the water droplet immediately after dripping a water droplet to sheet | seat A1. It is a photograph which shows the state of the water droplet after 10 second passage from the time of dropping a water droplet on the sheet A1. 4 is a photograph showing a state of water droplets immediately after dropping water droplets on a sheet Z. 3 is a photograph showing a state of water droplets after 10 seconds from the time when water droplets were dropped on a sheet Z. FIG. It is a SEM image of porous carbon used for sheet A1. It is a photograph when an external force is applied to the sheet A1 in the bending direction. 3 is a graph showing pore distribution curves of sheets A1 and Z.

The present invention is characterized by comprising a porous carbon powder having mesopores, in which adjacent mesopores communicate with each other, and a binder.
Since the sheet having such a structure can improve the corrosion resistance and the heat resistance, the temperature is high to some extent (about 300 to 500 ° C.) and is optimal for a filter, a spacer, etc. used in an oxidizing atmosphere. Used. Specifically, the advantage of the present invention will be described by taking the case of using as a gas filter as an example.

  Since the metal filter is inferior in corrosion resistance, it may be corroded, and it deforms at a high temperature (about 300 ° C. or higher) and cannot maintain its shape. In addition, ceramic filters have low alkali resistance and may be dissolved in an atmosphere where ammonia or the like is present, and oxide-based porous materials such as silica gel are hot (around 300 ° C). Since the structure is destroyed, the filter function cannot be fully demonstrated. Furthermore, in a filter using an activated carbon sheet, activated carbon burns at about 300 ° C., and therefore cannot be used at high temperatures. On the other hand, the filter using the sheet of the present invention is excellent in corrosion resistance and heat resistance and has mesopores. Therefore, even when used under harsh conditions (for example, at 300 ° C. or higher and in a high humidity atmosphere), it does not oxidize or burn, and sufficiently functions as a filter. can do.

In addition, the sheet of the present invention can be optimally used for a catalyst carrier and a gas diffusion layer of a fuel cell that can rise to about 300 ° C. For example, when used as a catalyst carrier for a fuel cell, the sheet of the present invention is superior in wettability as compared with an activated carbon sheet, and therefore exhibits the following effects. When an activated carbon sheet is used as the catalyst carrier of the fuel cell, the activated carbon sheet is inferior in wettability, so that a water film is formed on the sheet surface. Accordingly, since the platinum and O ₂ gas is a catalyst hardly contacts, catalytic activity is not sufficiently exhibited. On the other hand, when the sheet of the present invention is used as a catalyst carrier for a fuel cell, the sheet of the present invention is excellent in wettability, so that it is possible to suppress the formation of a water film on the sheet surface. Therefore, since the catalyst platinum and O ₂ gas can be easily contacted, the catalytic ability is sufficiently exhibited.

Furthermore, since the present invention is sheet-like and dust generation and the like are suppressed, handling becomes easy. Moreover, since the sheet of the present invention has flexibility, it is excellent in workability when it is incorporated into a part, collected from a part, and the like.
In the present specification, a mesopore means a pore having a pore diameter of 2 nm or more and 50 nm or less, and a micropore means a pore less than 2 nm.

The ratio of the binder to the porous carbon powder is desirably 5% by weight or more and 50% by weight or less.
When the ratio is less than 5% by weight, dust may be generated or the shape may be lost. On the other hand, when the ratio exceeds 50% by weight, the binder may be a main material, and thus flexibility may be reduced.

The film thickness is desirably 250 μm or more and 1000 μm or less.
If the film thickness is less than 250 μm, the shape may not be maintained as a self-supporting sheet. On the other hand, when the film thickness exceeds 1000 μm, the flexibility may decrease.

The binder is preferably a binder containing at least one atom of nitrogen and / or fluorine, and particularly preferably polytetrafluoroethylene.
If the binder contains 1 atom or more of nitrogen and / or fluorine, the sheet of the present invention can be used up to about 420 ° C. If the binder is polytetrafluoroethylene, the sheet of the present invention can be used up to about 500 ° C.

Specific embodiments will be described below.
The porous carbon used in the present invention can be produced, for example, as follows. First, a fluid material containing an organic resin and an oxide (template particle) are wet or dry mixed in a solution or powder state to produce a mixture. Next, this mixture is carbonized at a temperature of, for example, 500 ° C. or higher in a non-oxidizing atmosphere or a reduced pressure atmosphere. Finally, the template particles are removed by washing, and thereby porous carbon can be produced. The porous carbon thus produced has a large number of pores (mesopores and micropores). The arrangement of the pores is not regular but has a structure in which they are randomly arranged (the mesopores are irregularly arranged).

  Here, the pore diameter, the pore distribution of the porous carbon, and the thickness of the carbonaceous wall can be adjusted by changing the diameter of the template particles and the type of the organic resin. Accordingly, it is possible to easily produce porous carbon having different pore diameters, specific surface areas, and the like by appropriately selecting the diameter of the template particles and the type of the organic resin.

Specifically, as the organic resin, a polyimide containing at least one nitrogen or fluorine atom in the unit structure is preferably used. The polyimide can be obtained by polycondensation of an acid component and a diamine component. However, in this case, it is necessary that one or both of the acid component and the diamine component contain one or more nitrogen atoms or fluorine atoms.
Specifically, a polyamic acid film which is a polyimide precursor is formed, and the solvent is removed by heating to obtain a polyamic acid film. Next, a polyimide can be manufactured by thermally imidating the obtained polyamic acid film at 200 ° C. or higher.

  Examples of the diamine include 2,2-bis (4-aminophenyl) hexafluoropropane [2,2-Bis (4-aminophenyl) hexafluoropropane], 2,2-bis (trifluoromethyl) -benzidine [2,2 ′. -Bis (trifluoromethyl) -benzidine], 4,4'-diaminooctafluorobiphenyl, 3,3'-difluoro-4,4'-diaminodiphenylmethane, 3,3'-difluoro-4,4'-diaminodiphenyl ether, 3,3′-di (trifluoromethyl) -4,4′-diaminodiphenyl ether, 3,3′-difluoro-4,4′-diaminodiphenylpropane, 3,3′-difluoro-4,4′-diaminodiphenyl Hexafluoropropane, 3,3'- Fluoro-4,4′-diaminobenzophenone, 3,3 ′, 5,5′-tetrafluoro-4,4′-diaminodiphenylmethane, 3,3 ′, 5,5′-tetra (trifluoromethyl) -4, 4'-diaminodiphenylmethane, 3,3 ', 5,5'-tetrafluoro-4,4'-diaminodiphenylpropane, 3,3', 5,5'-tetra (trifluoromethyl) -4,4'- Diaminodiphenylpropane, 3,3 ′, 5,5′-tetrafluoro-4,4-diaminodiphenylhexafluoropropane, 1,3-diamino-5- (perfluorononenyloxy) benzene, 1,3-diamino- 4-methyl-5- (perfluorononenyloxy) benzene, 1,3-diamino-4-methoxy-5- (perfluorononenyloxy) benzene, 1 3-diamino-2,4,6-trifluoro-5- (perfluorononenyloxy) benzene, 1,3-diamino-4-chloro-5- (perfluorononenyloxy) benzene, 1,3-diamino- 4-Pubromo-5- (perfluorononenyloxy) benzene, 1,2-diamino-4- (perfluorononenyloxy) benzene, 1,2-diamino-4-methyl-5- (perfluorononenyloxy) ) Benzene, 1,2-diamino-4-methoxy-5- (perfluorononenyloxy) benzene, 1,2-diamino-3,4,6-trifluoro-5- (perfluorononenyloxy) benzene, 1,2-diamino-4-chloro-5- (perfluorononenyloxy) benzene, 1,2-diamino-4-bromo-5- (perfluorononenyloxy) Xyl) benzene, 1,4-diamino-3- (perfluorononenyloxy) benzene, 1,4-diamino-2-methyl-5- (perfluorononenyloxy) benzene, 1,4-diamino-2- Methoxy-5- (perfluorononenyloxy) benzene, 1,4-diamino-2,3,6-trifluoro-5- (perfluorononenyloxy) benzene, 1,4-diamino-2-chloro-5 -(Perfluorononenyloxy) benzene, 1,4-diamino-2-pbromo-5- (perfluorononenyloxy) benzene, 1,3-diamino-5- (perfluorohexenyloxy) benzene, 1,3 -Diamino-4-methyl-5- (perfluorohexenyloxy) benzene, 1,3-diamino-4-methoxy-5- (perfluorohexenyl) Xyl) benzene, 1,3-diamino-2,4,6-trifluoro-5- (perfluorohexenyloxy) benzene, 1,3-diamino-4-chloro-5- (perfluorohexenyloxy) benzene, 1 , 3-Diamino-4-bromo-5- (perfluorohexenyloxy) benzene, 1,2-diamino-4- (perfluorohexenyloxy) benzene, 1,2-diamino-4-methyl-5- (perfluoro Hexenyloxy) benzene, 1,2-diamino-4-methoxy-5- (perfluorohexenyloxy) benzene, 1,2-diamino-3,4,6-trifluoro-5- (perfluorohexenyloxy) benzene, 1,2-diamino-4-chloro-5- (perfluorohexenyloxy) benzene, 1,2-diamino-4- Lomo-5- (perfluorohexenyloxy) benzene, 1,4-diamino-3- (perfluorohexenyloxy) benzene, 1,4-diamino-2-methyl-5- (perfluorohexenyloxy) benzene, 1, 4-diamino-2-methoxy-5- (perfluorohexenyloxy) benzene, 1,4-diamino-2,3,6-trifluoro-5- (perfluorohexenyloxy) benzene, 1,4-diamino-2 -Chloro-5- (perfluorohexenyloxy) benzene, 1,4-diamino-2-promo-5- (perfluorohexenyloxy) benzene, p-phenylenediamine (PPD) containing no fluorine atom, dioxydianiline An aromatic diamine such as The diamine component may be used in combination of two or more of the above aromatic diamines.

  Further, as the fluid material, it is desirable to use a resin that generates fluidity at a temperature of 200 ° C. or lower, or a varnish-like polymer resin. If a resin that generates fluidity at a temperature of 200 ° C. or less or a varnish-like polymer resin is used as the fluid material, the above-described porous carbon charcoal can be produced more smoothly.

  However, the flowable material is not limited to a resin or the like that generates fluidity at a temperature of 200 ° C. or less. Even if fluidity does not occur at a temperature of 200 ° C. or less, it is highly soluble in water or organic solvent. Any molecular material can be used in the present invention. Examples of such a material include PVA (polyvinyl alcohol), PET (polyethylene terephthalate) resin, imide resin, phenol resin, and the like.

Furthermore, it is more preferable to use a fluid material having a carbon yield of 40% to 85%. If the carbon yield of the fluid material is too small or large (specifically, if the carbon yield of the fluid material is less than 40% or exceeds 85%), the three-dimensional network structure is not retained. If a flowable material with a carbon yield of 40% or more and 85% or less is used, a three-dimensional network structure in which, after removing the template particles, the location where the template particles exist becomes continuous pores. This is because it is possible to reliably obtain porous carbon having the following. Further, if the same particle size is used as the template particle, continuous pores of the same size are formed, so that sponge-like and substantially yielding porous carbon can be produced.
Further, if the carbon yield of the fluid material is in the above range, the micropores are very developed, and the specific surface area is increased. However, even if the carbon yield of the flowable material is in the above range, micropores do not develop when template particles are not used.

On the other hand, as acid components, 4,4-hexafluoroisopropylidenediphthalic anhydride (6FDA) containing a fluorine atom and 3,4,3 ′, 4′-biphenyltetracarboxylic dianhydride containing no fluorine atom Product (BPDA), pyromellitic dianhydride (PMDA) and the like.
Examples of the organic solvent used as a solvent for the polyimide precursor include N-methyl-2-pyrrolidone and dimethylformamide.

The imidization method is shown in a known method (for example, see “New Polymer Experimental Science” edited by the Society of Polymer Science, Kyoritsu Shuppan, March 28, 1996, Volume 3, Synthesis and Reaction of Polymers (2), page 158). Thus, either heating or chemical imidization may be followed, and the present invention is not affected by this imidization method.
Furthermore, as the resin other than polyimide, petroleum-based tar pitch, acrylic resin, or the like can be used.

On the other hand, in addition to alkaline earth metal oxides (magnesium oxide, calcium oxide, etc.), the raw material used as the oxide is a metal organic acid (magnesium citrate, Magnesium oxalate, calcium citrate, calcium oxalate, etc.), chlorides, nitrates, sulfates can also be used.
Further, as the cleaning liquid for removing oxides, a general inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, citric acid, acetic acid, formic acid is used, and it is preferably used as a dilute acid of 2 mol / l or less. It is also possible to use hot water of 80 ° C. or higher.

  Further, the carbonization of the mixture is preferably performed at a temperature of 500 ° C. or higher and 1500 ° C. or lower in a non-oxidizing atmosphere or a reduced pressure atmosphere. Since the resin with a high carbon yield is a polymer, the carbonization may be insufficient at less than 500 ° C. and the pores may not be sufficiently developed. On the other hand, the shrinkage is large at 1500 ° C. or more, and the oxide is sintered and coarse. This is because the pore size is reduced and the specific surface area is reduced. The non-oxidizing atmosphere is an argon atmosphere or a nitrogen atmosphere, and the reduced pressure atmosphere is an atmosphere of 133 Pa (1 torr) or less.

  The bulk density of the porous carbon is preferably 0.07 g / cc or more and 1.0 g / cc or less. When the bulk density is less than 0.07 g / cc, it is difficult to secure a specific surface area, and the shape of the carbonaceous wall may not be maintained. On the other hand, when the bulk density exceeds 1.0 g / cc or less. It is difficult to form a three-dimensional network structure, and pore formation may be insufficient.

  Moreover, after mixing the porous carbon produced as described above and a binder, a porous carbon sheet can be produced by drying treatment and further pressing. In this case, polytetrafluoroethylene, polyimide, butadiene strubber, acrylic elastomer, or the like can be used as the binder. Among them, it is particularly preferable to use polytetrafluoroethylene.

Example 1
First, as shown in FIG. 1 (a), a magnesium oxide powder (MgO, average particle diameter is 5 nm) 2 as a template particle and an organic resin (polyvinyl alcohol) 1 as a carbon precursor are in a 3: 2 ratio. Mixed by weight. Next, as shown in FIG.1 (b), this mixture was heat-processed at 900 degreeC by inert atmosphere for 2 hours, and polyvinyl alcohol was thermally decomposed, and the baked product provided with the carbonaceous wall 3 was obtained. . Next, the obtained fired product was washed with a sulfuric acid solution added at a rate of 1 mol / l to completely elute MgO. As a result, an amorphous porous carbon powder 5 having a large number of pores 4 was obtained as shown in FIG.

  The porous carbon powder had an average particle size of 50 μm (particle size was 2 to 70 μm). Further, as shown in FIG. 10, in the porous carbon powder, mesopores are irregularly arranged in the carbonaceous wall, adjacent mesopores communicate with each other, and the carbonaceous wall has a three-dimensional structure. A network structure was formed.

Thereafter, the porous carbon powder and polytetrafluoroethylene (PTFE-6J manufactured by DuPont) as a binder are mixed at a weight ratio of 8: 2, stirred at room temperature, and then dried using a dryer. The mixture was dried at 120 ° C. for 5 hours to obtain a mixture of porous carbon powder and Teflon (registered trademark). Finally, the mixture was rolled using a rolling roll press (roll interval: 500 μm) to prepare a sheet having a specific surface area of 1200 m ² / g and a thickness of 500 μm.

The sheet thus produced is hereinafter referred to as sheet A1.
Here, when an external force was applied to the sheet A1 in the bending direction, the sheet A1 was bent as shown in FIG. 11 and returned to its original state when the application of the external force was stopped. From this, it was recognized that the sheet A1 has flexibility.

(Example 2)
A sheet was prepared in the same manner as in Example 1 except that polyimide was used instead of polytetrafluoroethylene as the binder. The specific surface area and thickness are the same as those in Example 1.
The sheet thus produced is hereinafter referred to as sheet A2.
In addition, it was recognized that the sheet A2 also has flexibility similar to the sheet A1.

(Comparative example)
A sheet was prepared in the same manner as in Example 2 except that commercially available activated carbon (manufactured by Wako Pure Chemical Industries, Ltd. (product number 037-02115)) was used as the carbon powder instead of the porous carbon powder. The specific surface area and thickness are the same as those in Example 1.
Hereinafter, such a sheet is referred to as a sheet Z.

(Experiment 1)
Since the thermogravimetric analysis measurement was performed in the air atmosphere of the sheets A1, A2, and Z, the results are shown in FIG. For reference, the measurement was also made for the case of only porous carbon used in Examples 1 and 2, and the results are also shown.

  As apparent from FIG. 2, the sheet Z has a weight reduction from the beginning of heating, and a significant weight reduction occurs at about 200 ° C. or more. In contrast, the sheets A1 and A2 did not lose weight unless the temperature was about 420 ° C. or higher. In particular, it was found that the sheet A1 did not lose weight up to about 500 ° C. and had better heat resistance than the case of only porous carbon.

(Experiment 2)
The sheets A1 and Z are alternately exposed to a dry N ₂ atmosphere and a wet N ₂ atmosphere, and after exposure to the dry N ₂ atmosphere causes a weight loss, how long the sheet A1 and Z are exposed to the wet N ₂ atmosphere is the original state (experiment Since it was investigated using the apparatus shown in FIG. 3 whether it returns to the state before a start), the result is shown in FIG.4 and FIG.5.

4 is a graph showing an experimental result in the sheet A1, and FIG. 5 is a graph showing an experimental result in the sheet Z. Moreover, the apparatus of FIG. 3 is an apparatus used for this experiment, and has the following structure. Both ends of the cylindrical body 11 are sealed with sealing bodies 12, 12. An N ₂ gas introduction pipe 13 is inserted into one sealing body 12 of these sealing bodies 12, 12, and one sealing body 12 has An N ₂ gas discharge pipe 16 is inserted. Inside the cylindrical body 1 is disposed a weight measuring table 14 on which a sheet can be placed and the weight of the sheet can be continuously measured. On the outside of the cylindrical body 11 is a heater for heating the sheet. 15 is arranged. Furthermore, the dry N ₂ atmosphere has a temperature of 25 ° C. and a humidity of about 1% or less, and the wet N ₂ atmosphere has a temperature of 25 ° C. and a humidity of about 85%.

As is clear from FIG. 5, the sheet Z does not return to its original state even after about 9 hours have passed since the introduction of the wet N ₂ , whereas the sheet A1 has a wet N ₂ as apparent from FIG. It was confirmed that the product returned to its original state in a very short time after introduction. In order to investigate the reason for such an experimental result, the following Experiment 3 was performed.

(Experiment 3)
The same amount of water droplets were dropped on the sheet A1 and the sheet Z, and the state of the water droplet immediately after dropping and the state of the water droplet after 10 seconds from the time of dropping were examined, and the results are shown in FIGS. Show. 6 is a photograph showing the state of the water drop immediately after dropping the water droplet on the sheet A1, FIG. 7 is a photograph showing the state of the water drop after 10 seconds from the time when the water drop is dropped on the sheet A1, and FIG. FIG. 9 is a photograph showing the state of the water drop after 10 seconds from the time when the water drop was dropped on the sheet Z. FIG. Moreover, in FIGS. 6-9, 21 is a sheet | seat and 22 is a water drop.

  As is apparent from FIGS. 8 and 9, in the sheet Z, the state of the water droplets does not change much immediately after the water droplets are dropped and 10 seconds after the water droplets are dropped, and moisture does not penetrate into the sheet. Is recognized. On the other hand, as is apparent from FIGS. 6 and 7, in the sheet A1, the moisture penetrates into the sheet immediately after the water droplet is dropped, and most of the moisture is 10 seconds after the water droplet is dropped. It is observed that the sheet penetrates. From these, it can be seen that the wettability of the sheet A1 is significantly improved as compared with the sheet Z.

Thus, the sheet A1 is excellent in wettability, as shown in Experiment 2 above, to return to the original state in a short time after introduction of wet N _2. On the other hand, since the sheet Z is inferior in wettability, it is considered that the sheet Z does not return to the original state over a long period of time after the introduction of the wet N ₂ as shown in Experiment 2 above. Note that it is considered that the sheet A2 also returns to the original state in a short time after the introduction of the wet N ₂ for the same reason as in the case of the sheet A1.

(Experiment 4)
Since the pore distribution of the sheets A1 and Z was examined, the result is shown in FIG. In the experiment, nitrogen was used as an adsorption gas, and the pore distribution was analyzed using a BJH method from a hot spring such as nitrogen adsorption measured at a temperature of 77K.
As is apparent from FIG. 12, the sheet A1 has a pore diameter distribution having a peak at a pore diameter of about 5 nm, and it can be seen that mesopores are present. In contrast, the sheet Z has a flat pore diameter distribution with no peak, and it can be seen that no mesopores are present.

  The present invention can be used as a gas filter, a gas diffusion layer, a spacer, a catalyst carrier, an electrode, or the like.

1: Polyamic acid resin 2: Magnesium oxide 3: Carbonaceous wall 4: Pore 5: Porous carbon 11: Cylindrical body 12: Sealing body 13: N ₂ gas introduction pipe 14: Weight measuring table 15: Heater 16: N ₂ Gas discharge pipe 21: Sheet 22: Water droplet

Claims (5)

  A porous carbon sheet comprising mesopores and porous carbon powder in which adjacent mesopores communicate with each other and a binder.   The porous carbon sheet according to claim 1, wherein a ratio of the binder to the porous carbon powder is 5 wt% or more and 50 wt% or less.   The porous carbon sheet of Claim 1 or 2 whose film thickness is 250 micrometers or more and 1000 micrometers or less.   The porous carbon sheet according to any one of claims 1 to 3, wherein the binder is a binder containing one atom or more of nitrogen and / or fluorine.   The porous carbon sheet according to claim 4, wherein the binder containing at least one atom of nitrogen and / or fluorine is polytetrafluoroethylene.

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