JP4728142B2 - Method for producing carbon airgel powder - Google Patents

Description

  The present invention relates to a method for producing a carbon airgel powder. The carbon airgel powder produced by this method is suitable for use in electrode materials such as capacitors, adsorbents, column fillers, and catalyst carriers such as fuel cells.

  Conventionally, a carbon airgel powder produced using a polymer of dihydroxybenzene and formaldehyde as a starting material is known (Patent Document 1).

This carbon airgel powder is manufactured by the process shown in FIG.
(Polymerization step S91)
That is, as polymerization step S91, dihydroxybenzene such as resorcinol and catechol and formaldehyde are polymerized in the presence of sodium carbonate to obtain an organic wet gelled product.

(Solvent replacement step S92)
Next, as a solvent replacement step S92, the gelled product is washed with a water-soluble organic solvent such as methanol or acetone, and the water contained in the gelled product is replaced with a water-soluble solvent.

(Supercritical drying step S93)
Further, as the supercritical drying step S93, the solvent-substituted gelled product is put into a stainless steel pressure vessel, CO2 is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then CO2 is slowly discharged. To shift the CO2 to the gas phase condition and perform supercritical drying. The gelled product thus dried is composed of primary particles forming a network structure having a particle size of 0.1 microns or less, and the bulk density is extremely small at 100 mg / ml. This is because in supercritical drying, unlike normal drying, drying does not involve shrinkage due to capillary force, so that the pore structure formed by crosslinking with formaldehyde in the polymerization step S1 remains intact without being destroyed. It is thought that it remains.

(Pyrolysis step S94)
Then, as the pyrolysis step S94, the dried gelled product is heated to a high temperature under a nitrogen atmosphere to obtain a carbide lump. The carbide thus obtained maintains the pore structure before carbonization.

(Crushing step S95)
Finally, in the pulverization step S95, the above-mentioned carbide mass is pulverized by a pulverizer to obtain a carbon airgel powder.

  Since the carbon airgel powder thus obtained can have a very small particle size, when used as an electrode in a polymer electrolyte fuel cell, the thickness of the electrode can be reduced. Further, since the carbide obtained by pyrolysis of the dried gelled product has a pore structure, the carbon aerogel obtained by pulverizing the carbide is expected to have excellent gas permeability. For this reason, it has also been proposed to use carbon aerogel as an electrode of a polymer electrolyte fuel cell (Patent Document 2).

U. S. patent No. 4873218 claim14, 15 Japanese National Patent Publication No. 11-503267

  However, when the inventors conducted a detailed test on the carbon aerogel described in Patent Document 1, the carbide obtained in the pyrolysis step S94 in FIG. 1 has a pore structure, but this is pulverized. The carbon airgel obtained in this way was found to have almost destroyed its pore structure.

  The present invention has been made in view of the above-described conventional situation, and should solve the problem of providing a method for producing a carbon airgel powder in which the pore structure once formed in the production process remains with almost no destruction. It is an issue.

  As a result of intensive studies to solve the above problems, the inventors have crushed the organic wet gelled product obtained in the polymerization step in water before solvent replacement, and then performed the solvent replacement step, supercritical drying. By performing the process and the pyrolysis process, it was found that a carbon airgel powder in which the pore structure once formed in the production process was maintained as it was was obtained, and the present invention was completed.

  That is, the method for producing the carbon airgel powder of the first aspect of the present invention includes a step of obtaining an organic wet gelled product, a pulverizing step of pulverizing the organic wet gelled product into a gel slurry, and the gel slurry as a water-soluble organic solvent. Solvent replacement step of performing solvent replacement by contact, a supercritical drying step of obtaining a gel dry powder by supercritical drying of the solvent-substituted gel slurry, and heat for thermally decomposing the gel dry powder into a carbon aerogel powder A decomposition step.

  In such a method for producing a carbon airgel powder, the organic wet gelled product is pulverized in the pulverizing step and then the solvent is replaced. For this reason, it will grind | pulverize in the state in which water was contained in the pore of the gelled material, and compared with the grinding | pulverization in a dry state, a pore is protected by the cushion effect of water, and it will become difficult to destroy. In addition, since the organic wet gelled product is pulverized in advance, the solvent replacement time is also shortened. For this reason, the carbon airgel powder obtained by the production method of the present invention maintains the pore structure reflecting the pore structure of the gelled product. For this reason, it can be suitably used as an electrode material in a polymer electrolyte fuel cell.

According to the invention of the second aspect, the organic wet gelled product is obtained by polymerizing polyhydroxybenzene and formaldehyde in the presence of a base catalyst.
Here, polyhydroxybenzene means a compound having two or more hydroxyl groups in the benzene ring. Such a compound can be easily polymerized with formaldehyde to form a network structure and form a pore structure.

According to the invention of the third aspect, dihydroxybenzene and / or a dihydroxybenzene derivative is employed as the polyhydroxybenzene.
Among polyhydroxybenzenes, dihydroxybenzene and dihydroxybenzene derivatives are relatively stable compounds, and are therefore easy to handle and suitable.
Particularly preferred as dihydroxybenzene is resorcinol. Therefore, as the invention of the fourth aspect, resorcinol was adopted as dihydroxybenzene.

According to the fifth aspect of the invention, the water-soluble organic solvent used in the solvent replacement step employs one or more mixed solvents of methanol, acetone, and amyl acetate.
The water-soluble organic solvent used in the solvent replacement step is preferably a mixed solvent of one or more of methanol, acetone and amyl acetate. In this case, water contained in the gelled product can be easily replaced with a solvent.

According to the invention of the sixth aspect, the pulverization of the organic wet gelled product in the pulverization step is performed using a medium.
According to the test results of the present inventors, when the organic wet gelled material is pulverized using a medium, the particle diameter of the carbon aerogel is controlled by appropriately selecting the pulverization conditions such as the diameter of the medium and the pulverization time. , The pore structure can be retained. For this reason, the carbon airgel of the desired characteristic according to a use can be obtained.
Of course, other pulverization methods that do not use media in advance (for example, a pulverization method using a rotary pulverizer that does not use a homogenizer or media) can be performed before performing the pulverization step using media. This is because if the pulverization process is performed using media at the final stage of the pulverization process, the particle size of the carbon airgel can be controlled and the pore structure can be maintained.
Moreover, there is no limitation in particular about the material of media, Stabilized zirconia, an alumina, agate, quartz etc. can be used. Since the fine powder of media may enter the carbon airgel powder as an impurity, it is preferable to appropriately select a media material that does not have an adverse effect depending on the use of the carbon airgel powder.

According to the seventh aspect of the invention, the diameter of the media is 5 mm or less.
According to the test results of the present inventors, when the diameter of the media is 5 mm or less, a gel powder having a small particle diameter can be obtained, and the pore structure is not easily destroyed. For this reason, the particle diameter of the carbon airgel powder finally obtained can be small, and the pore structure of the organic wet gelled product can be maintained. More preferable is a medium having a diameter of 0.65 mm or less.

According to the invention of the eighth aspect, the pulverization step is performed by controlling at least the diameter of the media and the pulverization time.
According to the test results of the present inventors, it has been found that the particle diameter and pore distribution of the carbon airgel powder obtained by the present invention are closely related to the diameter of the media and the grinding time. For this reason, if the grinding | pulverization process is performed by controlling the diameter and grinding | pulverization time of a medium, the carbon airgel of the desired characteristic according to a use can be obtained with sufficient reproducibility.

According to the ninth aspect of the invention, the pulverization step is performed by controlling the media diameter and the pulverization time so that the average particle diameter of the finally obtained carbon airgel powder does not become less than 1 micron.
According to the test results of the present inventors, a large change appears in the pore distribution when the average particle diameter of the carbon airgel powder is 1 micron as a boundary. In other words, when the pulverization time is lengthened to obtain a carbon airgel powder having a diameter smaller than 1 micron or the diameter of the media is reduced, the pore structure is destroyed even if the particle diameter is reduced. The pore volume fraction is slightly reduced. For this reason, if the diameter of the media and the pulverization time are controlled so that the average particle diameter of the carbon airgel powder does not become less than 1 micron, a carbon airgel powder having a sufficiently maintained pore distribution can be obtained.

Hereinafter, Examples 1 and 2 embodying the present invention will be described in comparison with Comparative Examples 1 and 2.
(Example 1)
Polymerization step S1
In Example 1, as shown in FIG. 2, 4 g of resorcinol, 5.5 ml of formaldehyde 37% aqueous solution, and 0.019 g of sodium carbonate 99.5% powder were mixed in the polymerization step S1, and stirred for 3 hours. A gelled product was obtained by aging at room temperature -24h, 50 ° C-24h, 90 ° C-72h.

Grinding step S2
The gelled product was decanted with ion-exchanged water, and then pulverized for 2 hours with a planetary rotating ball mill in the presence of water to obtain a gel powder slurry.

Solvent replacement step S3
And as solvent substitution process S3, after wash | cleaning the said gel powder slurry 5 times with acetone by the suction filtration method, the slurry was made into the cake layer type | mold.

Supercritical drying process S4
Further, as the supercritical drying step S4, the solvent-substituted gel powder is put into a stainless steel pressure vessel, CO2 is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then CO2 is slowly discharged. Thus, CO2 was transferred to gas phase conditions and supercritical drying was performed to obtain a gel dry powder.

Thermal decomposition process S5
Finally, as the pyrolysis step S5, the gel dry powder was put in an electric furnace, heated in a nitrogen atmosphere at 1000 ° C. for 4 hours, and then cooled to obtain a carbon airgel powder.
The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 629 m ² / g
Pore volume: 2.00 cm ³ / g

(Example 2)
In Example 2, the grinding time in the grinding step S2 was 4 hours. Other conditions are the same as those in the first embodiment, and the description is omitted.
The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 632 m ² / g
Pore volume: 1.83 cmcm ³ / g

(Comparative Example 1)
In Comparative Example 1, after performing the pyrolysis step S5 without performing the pulverization step S2 in Example 1, the obtained bulk carbon airgel was used as a measurement sample. Other conditions are the same as those in the first embodiment, and the description is omitted. The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 670 m ² / g
Pore volume: 2.17 cm ³ / g

(Comparative Example 2)
In Comparative Example 2, the massive carbon aerogel obtained in Comparative Example 1 was pulverized for 2 hours at a revolution of 300 rpm and a rotation of 300 rpm by a planetary rotating ball mill, and the obtained powder was used as a measurement sample. The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 105 m ² / g
Pore volume: 0.25 cm ³ / g

<Evaluation>
For the carbon aerogels of Example 1 and Comparative Examples 1 and 2, the pore distribution was measured by the BET adsorption method. As a result, as shown in FIG. 3, the carbon aerogel of Example 1 has almost no difference in pore distribution compared with Comparative Example 1 in which no pulverization is performed, and the pore structure is not broken. I found out that I was leaning.

  On the other hand, in Comparative Example 2, as shown in FIG. 4, it can be seen that the pores are reduced and the pore structure is almost destroyed.

  Moreover, the particle size distribution of the gel dry powder immediately after performing supercritical drying and the carbon aerogel immediately after pyrolysis in Example 1 and Example 2 was measured. As a result, as shown in FIGS. 5 and 6, it was found that the particle size distribution of the carbon airgel can be controlled by controlling the pulverization time in the pulverization step S2. It was also found that the gel powder slurry and the carbon airgel powder showed almost the same particle size distribution.

  Further, the pore distribution of the carbon airgel powders of Example 1 and Example 2 was measured by the BET adsorption method. As a result, as shown in FIG. 7, there is a difference in the pore distribution between Example 1 and Example 2, and the pore distribution of the carbon airgel can be controlled by controlling the grinding time in the grinding step S2. Further confirmed.

(Example 3 to Example 14)
In Example 3 to Example 14, the relationship between the pulverization condition of the gelled product and the characteristics of the obtained carbon airgel powder was examined. The grinding process was performed in three stages as shown in FIG. That is, as a first pulverization step, the gelled product obtained in the polymerization step S1 in Example 1 is pulverized with a homogenizer (rotation speed 2000 rpm, pulverization time 15 minutes). Next, as a second pulverization step, the pulverized material obtained in the first pulverization step is placed in a container of a planetary rotating ball mill, and further, a 5 mm diameter stabilized zirconia-made medium is pulverized (revolution 255 rpm, rotation 550 rpm). , Grinding time 2 hours). Further, as a third pulverization step, crushed by a planetary rotating ball mill was performed using stabilized zirconia media having various diameters to obtain gel powder slurry. Table 1 shows the pulverization conditions of Examples 3 to 14 in the third pulverization step. Thus, after performing the 1st-3rd grinding | pulverization process, the solvent substitution process S2, the supercritical drying process S3, and the thermal decomposition process S4 similar to Example 1 and Example 2 were performed, and the carbon airgel powder was obtained.

(Relationship between media diameter and arbitrary particle diameter)
About the gel powder slurry which concerns on Example 3-Example 14 obtained at the 3rd grinding | pulverization process, the particle size distribution measurement by a laser diffraction and a scattering system was performed. The results are shown in FIG. From this figure, it was found that when the diameter of the media used in the third pulverization step was reduced, the arbitrary% particle size was reduced. Further, it was found that the arbitrary% particle size is reduced when the pulverization time of the third pulverization step is increased. From the above results, it was found that a carbon airgel powder having a desired particle size according to the purpose can be obtained by controlling the pulverization time and the media diameter.

(Relationship between media diameter, total pore volume and BET specific surface area)
About the carbon airgel powder obtained in Examples 3 to 14, the total pore volume and the BET specific surface area were measured by a nitrogen adsorption method (FIG. 10). As a result, there was little difference due to the difference in the third pulverization process.

(Relationship between average particle size and pore volume fraction of gel powder slurry)
About the gel powder slurry obtained in Example 3 to Example 14, the average particle diameter and the pore volume fraction of 10 to 30 nm (10 to 30 nm with respect to the mesopore volume determined from the desorption side of the nitrogen adsorption isotherm) The ratio of pore volume) was plotted. As a result, as shown in FIG. 11 and FIG. 12, it was found that the pore volume fraction rapidly decreases when the average particle size of the gel powder slurry is less than 1 micron. This shows that it is difficult to damage the pore structure if the pulverization conditions are appropriately controlled so that the particle size of the gel powder slurry does not become less than 1 micron. Further, it can be seen from FIG. 11 that the pore volume fraction decreases according to the pulverization time in the third pulverization step. Further, FIG. 12 shows that the pore volume can be maintained by adjusting the pulverization time if the diameter of the medium is 5 mm or less. It can also be seen that if the media diameter is 0.65 mm or less, it is easier to maintain the pore volume.

(Relationship between average particle size of gel powder slurry and pore volume fraction of carbon airgel powder)
FIG. 13 shows the result of plotting the diameter of the media used in the third pulverization step in Examples 3 to 14 and the pore volume fraction of the obtained carbon airgel powder. From this figure, it can be seen that when the media diameter is 5 mm or less, the pore volume fraction does not change so much and the pore structure is easily maintained. It can also be seen that the pore volume fraction is particularly well maintained when the media diameter is 0.3 mm and 0.65 mm.

  From the above results, it can be seen that the particle size and pore distribution of the carbon airgel powder are closely related to the media diameter and the grinding time. It can be seen that if the pulverization process is performed while controlling the diameter of the media and the pulverization time, a carbon airgel powder having desired characteristics according to the application can be obtained with good reproducibility.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

It is process drawing which shows the manufacturing method of the conventional carbon airgel powder. It is process drawing which shows the manufacturing method of the carbon airgel powder of an Example. 2 is a graph showing the pore distribution of Example 1 and Comparative Example 1. 6 is a graph showing the pore distribution of Comparative Example 1 and Comparative Example 2. It is a graph which shows the particle size distribution of the gel powder slurry after performing grinding | pulverization process S2 in Example 1 and Example 2. FIG. It is a graph which shows the particle size distribution of the carbon airgel powder thermally decomposed after performing supercritical drying in Example 1 and Example 2. It is a graph which shows the pore distribution of the carbon airgel powder of Example 1 and Example 2. It is process drawing of the grinding | pulverization process in Examples 3-14. It is a graph which shows the relationship between the media diameter in Examples 3-14, and the arbitrary% particle diameter of a gel powder slurry. It is a graph which shows the relationship between the media diameter in Examples 3-14, the total pore volume of a carbon airgel powder, and a BET specific surface area. It is a graph which shows the relationship between the average particle diameter of the gel powder slurry in each grinding | pulverization time in Examples 3-14, and the pore volume fraction of carbon airgel powder. It is a graph which shows the relationship between the average particle diameter of the gel powder slurry in each media diameter in Examples 3-14, and the pore volume fraction of carbon airgel powder. It is a graph which shows the relationship between the media diameter in each grinding | pulverization time in Examples 3-14, and the pore volume fraction of carbon airgel powder.

Explanation of symbols

S1 ... polymerization step S2 ... grinding step S3 ... solvent replacement step S4 ... supercritical drying step S5 ... pyrolysis step

Claims (9)

Obtaining an organic wet gelled product;
A pulverizing step of pulverizing the organic wet gelled product to form a gel powder;
A solvent replacement step of contacting the gel powder with a water-soluble organic solvent to perform solvent replacement;
A supercritical drying step of obtaining a gel dry powder by supercritical drying the solvent-substituted gel powder;
And a pyrolysis step of pyrolyzing the gel dry powder to obtain a carbon airgel powder.   The method for producing a carbon airgel powder according to claim 1, wherein the organic wet gelled product is obtained by polymerizing polyhydroxybenzene and formaldehyde in the presence of a base catalyst.   The method for producing a carbon airgel powder according to claim 2, wherein the polyhydroxybenzene is dihydroxybenzene and / or a dihydroxybenzene derivative.   The method for producing a carbon airgel powder according to claim 3, wherein the dihydroxybenzene is resorcinol.   5. The carbon airgel powder according to claim 1, wherein the water-soluble organic solvent used in the solvent replacement step is one or a mixed solvent of methanol, acetone, and amyl acetate. Production method.   The method for producing a carbon airgel powder according to any one of claims 1 to 5, wherein the pulverization of the organic wet gelled product in the pulverization step is performed using a medium.   The method for producing a carbon airgel powder according to claim 6, wherein the diameter of the medium is 5 mm or less.   The method for producing a carbon airgel powder according to any one of claims 1 to 7, wherein the pulverization step is performed by controlling at least the diameter of the media and the pulverization time to retain the pores of the carbon airgel.   9. The method for producing a carbon airgel powder according to claim 8, wherein the pulverization step is performed by controlling the diameter of the media and the pulverization time so that the average particle diameter of the finally obtained carbon airgel powder does not become less than 1 micron. .

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