JP2006306639A - Carbon aerogel, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide carbon aerogel maintaining pore characteristics in the production process, and also having a minute particle diameter in a specified range. <P>SOLUTION: The method for producing carbon aerogel includes: a sol preparation stage S1 where resorcinol, a formaldehyde aqueous solution and sodium carbonate are mixed and stirred to obtain an organic wetting sol; a membrane emulsification stage S2 where the organic wetting sol is emulsified by an SPG (Shirasu Porous Glass) membrane emulsification process, so as to form sol particulates; a polymerization stage S3 where the sol particulates are polymerized to form gel particulates; a solvent substitution stage S4 where the gel particulates are brought into contact with a water-soluble organic solvent in order to perform solvent substitution; a supercritical drying stage S5 where the gel particulates subjected to the solvent substitution are subjected to supercritical drying, so as to obtain gel dry powder; and a thermal decomposition stage S6 where the gel dry powder is thermally decomposed to obtain the carbon aerogel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbon airgel and a method for producing the same.

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

  This carbon aerogel is manufactured by the following steps 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)
Furthermore, in the supercritical drying step S93, the solvent-substituted gelled product is put into a stainless steel pressure vessel, CO ₂ is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then CO ₂ is slowly discharged. Thus, CO ₂ is transferred to gas phase conditions to 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 is performed without shrinkage due to capillary force, so that the pore structure formed by crosslinking with formaldehyde in the polymerization step S91 remains intact. 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, as the pulverization step S95, the carbide mass is pulverized by a pulverizer to obtain a powdered carbon aerogel.

  It has been proposed that the carbon airgel thus obtained is used as an electrode of a polymer electrolyte fuel cell (Patent Document 2). In this case, since the carbide obtained by pyrolysis of the dried gelled product has a pore structure, the powdered carbon aerogel obtained by pulverizing this also has excellent gas permeability. Therefore, it is expected that the fuel cell will exhibit excellent power generation efficiency. In addition, since the particle size of the carbon airgel can be made extremely small, the thickness of the cathode and anode catalyst layers can be reduced. Therefore, the cathode and anode electrodes and thus the thickness of the fuel cell must be reduced. You can also.

U.S. Pat. No. 4,873,218 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 by the pyrolysis step S94 in FIG. 8 has a pore structure. It turned out that the pore structure of the carbon aerogel obtained by pulverization using a pulverizer is almost destroyed.

  Moreover, the carbon airgel thus pulverized is only fine to the submicron level. In particular, the carbon airgel after pulverization has a distribution in which the particle diameter is wide to some extent. For this reason, if it is going to classify the thing of the particle diameter in a specific range from the carbon airgel with which the particle diameter is not uniform, a yield will be very bad.

  On the other hand, as a method other than pulverization, if an attempt is made to reduce the particle size of carbon aerogel by “emulsion synthesis method” by shearing force such as ultrasonic waves, a certain amount of surfactant must be used for emulsion polymerization. Don't be. And if the usage-amount of this surfactant increases, the pore characteristic of carbon airgel will change by the influence.

  The present invention has been made in view of the above-described conventional situation, and it is a problem to be solved to provide a carbon aerogel that maintains the pore characteristics of the manufacturing process and has a particle size within a minute specific range. It is said.

The method for producing a carbon airgel of the present invention includes a first step of obtaining an organic wet solubilized product,
A second step of emulsifying the organic wet solubilized product by a membrane emulsification method into sol fine particles;
A third step of polymerizing the sol fine particles to form gel fine particles;
A fourth step in which the gel fine particles are contacted with a water-soluble organic solvent to perform solvent substitution;
A fifth step of supercritical drying the solvent-substituted gel fine particles to obtain a gel dry powder;
And a sixth step of thermally decomposing the gel dry powder into a carbon aerogel.

  In such a method for producing a carbon aerogel, an organic wet sol compound is emulsified by a membrane emulsification method to form sol fine particles, the sol fine particles are polymerized to form gel fine particles, and the gel fine particles are replaced with a solvent. Then, after the solvent-substituted gel fine particles are supercritically dried to obtain a gel dry powder, the gel dry powder is pyrolyzed to obtain a carbon aerogel.

  Here, the membrane emulsification method is an emulsification technique for producing an emulsion by press-fitting a dispersed phase liquid into a continuous phase liquid through a membrane having pores.

  Thus, since the method for producing a carbon aerogel of the present invention does not have a conventional pulverization step after pyrolysis, the pore structure of the gel fine particles obtained by the membrane emulsification method is not destroyed, and it remains as it is. A maintained carbon aerogel can be obtained.

  In addition, since the sol fine particles obtained by the membrane emulsification method pass through the pores of the membrane and become fine particles, the particle diameter can be made fine by selecting and controlling the pores of the membrane. Further, variation in particle diameter can be reduced. In particular, if the pore diameter of the film is uniform, the obtained sol fine particles are also monodispersed particles having a uniform particle diameter. For this reason, the carbon airgel obtained by polymerizing, solvent substitution, supercritical drying and thermal decomposition of the sol fine particles also has a fine particle diameter within a specific range. For this reason, it is not necessary to classify the obtained carbon airgel, and the yield can be greatly improved.

  In addition, this carbon aerogel production method employs a membrane emulsification method, so that the amount of the surfactant used can be greatly reduced or not used at all. For this reason, the problem that the pore characteristics of the carbon airgel change due to the large amount of the surfactant used can be prevented.

  Therefore, the method for producing a carbon aerogel of the present invention can provide a carbon aerogel that maintains the pore characteristics in the production process and has a particle diameter within a minute specific range.

  In the carbon airgel production method of the present invention, the membrane emulsification method is preferably an SPG (Shirasu Porous Glass) membrane emulsification method.

The SPG film is a film of shirasu porous glass (Al ₂ O ₃ SiO ₂ -based glass porous body) generated from shirasu, lime and boric acid, and a large number of pores having a uniform diameter are formed in the film. Yes. The SPG film can be formed by selecting pores having a uniform diameter in a specific range within a range of about 50 nm to 20 μm. Moreover, although this SPG film is porous, it has very high mechanical strength and is excellent in heat resistance and heat insulation. Furthermore, this SPG film has excellent chemical resistance against most chemicals except strong alkali and hydrofluoric acid.

  By pressing the organic wet solubilized product into the continuous phase liquid through this SPG film, sol fine particles having a particle size within a minute specific range can be obtained with certainty. And if this sol fine particle is polymerized, it will become a gel fine particle with the particle diameter in the minute specific range. For this reason, in this case, the effects of the present invention can be reliably achieved.

  In the method for producing a carbon airgel of the present invention, the gel fine particles are preferably 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. According to the test results of the inventors, such a compound can be easily polymerized with formaldehyde to form a stitch-like structure and have a pore structure.

  In the method for producing a carbon airgel of the present invention, the polyhydroxybenzene is preferably dihydroxybenzene and / or a dihydroxybenzene derivative.

  Among polyhydroxybenzenes, dihydroxybenzene and dihydroxybenzene derivatives are relatively stable compounds and are therefore easy to handle and are preferable.

  In the method for producing a carbon airgel of the present invention, the dihydroxybenzene is preferably resorcinol. The inventors confirmed the effect on resorcinol.

  In the method for producing carbon airgel of the present invention, the water-soluble organic solvent is preferably a mixed solvent of one or more of methanol, acetone and amyl acetate. In this way, water and solvent contained in the gel fine particles can be easily replaced.

  The carbon aerogel of the present invention is obtained by emulsifying an organic wet solated product by a membrane emulsification method to form sol fine particles, polymerizing the sol fine particles to form gel fine particles, and contacting the gel fine particles with a water-soluble organic solvent to perform solvent substitution. Thereafter, the gel fine particles after solvent substitution are supercritically dried to obtain a gel dry powder, and the gel dry powder is obtained by thermal decomposition.

  When the carbon airgel thus obtained is used as an electrode in a polymer electrolyte fuel cell, the carbon airgel maintains the pore characteristics of the manufacturing process, and thus has excellent gas permeability. Truly demonstrates excellent power generation efficiency. Moreover, since the carbon airgel has a particle diameter in a minute specific range, the thickness of the electrode can be reduced, and the thickness of the fuel cell can also be reduced.

  Hereinafter, Test Example 1 will be described with reference to the drawings.

(Test Example 1)
Carbon airgel was manufactured using the manufacturing method of Examples 1-3 as follows.

  In the production methods of Examples 1 to 3, the organic wet sol compound was emulsified by a film emulsification method to form sol fine particles, and the sol fine particles were polymerized to form gel fine particles. Gel fine particles are supercritically dried to obtain a gel dry powder, and the gel dry powder is thermally decomposed to obtain a carbon aerogel. Specifically, it is manufactured by the following steps shown in FIG. In addition, the main test conditions of the manufacturing method of the carbon airgel of Examples 1-3 are put together in Table 1, and are shown.

(Sol adjustment step S1)
First, as a sol adjustment step Sl, 4 g of resorcinol, 5.5 ml of 37% formaldehyde aqueous solution, 0.019 g of 99.5% sodium carbonate powder, and 16 ml of dispersion medium: ion-exchanged water are mixed and stirred for 3 hours. Then, an organic wet gelled product was obtained by allowing a predetermined pre-emulsion polymerization time to elapse at a predetermined temperature (room temperature). In addition, the polymerization time before membrane emulsification differs in Examples 1 to 3, and is shown in Table 1.

(Membrane emulsification step S2)
In the film emulsification step S2, the SPG film emulsification apparatus 10 shown in FIG. 2 is used. The SPG membrane emulsification device 10 is positioned with the dispersed phase liquid storage tank 11, the dispersed phase liquid supply pipe 12 extending downward from the bottom of the dispersed phase liquid storage tank 11, and the lower end side of the dispersed phase liquid supply pipe 12 as the center. As shown in the figure, a continuous phase liquid storage tank 15 disposed below the dispersed phase liquid storage tank 11 and a lower end side of the dispersed phase liquid supply pipe 12 are inserted, and a cylindrical shape located at the center of the dispersed phase liquid storage tank 11. The SPG film 13 is provided.

  The dispersed phase liquid storage tank 11 stores the dispersed phase liquid 20. The upper part of the dispersed phase liquid storage tank 11 is not open to the atmosphere, and a pipe 18 for supplying a high-pressure gas such as nitrogen gas is connected thereto. The pipe 18 has a pressure adjusting valve 18a and a pressure gauge 18b, and adjusts the supply pressure of the pressurized gas to a predetermined pressure to pressurize the dispersed phase liquid 20 in the dispersed phase liquid storage tank 11. It is possible.

  The lower end of the dispersed phase liquid supply pipe 12 is sealed, and a plurality of discharge holes 12 a for supplying the dispersed phase liquid 20 to the cylindrical interior 13 a of the SPG film 13 are formed on the lower end side of the pipe wall. .

  The SPG film 13 shown enlarged in FIG. 3 is a shirasu porous glass film, and a large number of pores 13b having a uniform diameter are formed in the film. An example of the pore characteristics of the SPG membrane is shown in FIG. As the SPG film 13 of Test Example 1, one having a large number of pores having a uniform diameter of about 1 μm is used.

  As shown in FIG. 2, O-rings 14 are arranged on the upper and lower edges of the SPG film 13, and the lower end side of the dispersed phase liquid supply pipe 12, the upper and lower cylindrical edges of the SPG film 13, It is designed to seal between.

  The continuous phase liquid storage tank 15 stores the continuous phase liquid 30. The continuous phase liquid storage tank 15 is placed on the stirrer 16, and the rotor 16 a disposed at the bottom of the dispersed phase liquid storage tank 11 is driven by the stirrer 16 and rotates to rotate the continuous phase liquid 30. It is possible to stir.

  In the SPG membrane emulsification apparatus 10 having such a configuration, the dispersed phase liquid 20 in the dispersed phase liquid storage tank 11 is pressurized by a high pressure gas, and the SPG film is passed through the dispersed phase liquid supply pipe 12 and the discharge hole 12a. 13 cylinder interiors 13a. Then, as shown in FIG. 3, when the dispersed phase liquid 20 passes through the pores 13b of the SPG film 13 and is pressed into the continuous phase liquid 30, sol fine particles 21 having a uniform particle diameter are formed. Become.

  At this time, by adjusting the supply pressure of the high-pressure gas supplied into the dispersed phase liquid storage tank 11 within an appropriate pressure range, the particle diameter of the sol fine particles 21 obtained using the same SPG film 13 is adjusted to some extent. It is possible to adjust within the range. From the experience side, it is known that the particle diameter Dp of the sol fine particles 21 obtained by using the SPG film 13 having the pore diameter De is about three times the pore diameter De (Dp≈De × 3). .

  In Test Example 1, the organic wet sol-form was used as the dispersed phase liquid 20. Further, as the continuous phase liquid 30, a mixed liquid of 50 ml of cyclohexane and a surfactant (sorbitan monooleate) was used. About the quantity of surfactant, it differs in Examples 1-3, and it shows in Table 1 collectively.

  In this way, in the film emulsification step S2, the sol particles adjusted in the sol adjustment step S1 are emulsified by the film emulsification method by using the SPG film emulsification apparatus 10 to obtain the sol fine particles 21.

(Polymerization step S3)
In the polymerization step S3, the sol fine particles were left to stand for about 24 hours as they were, and the sol fine particles were polymerized to form gel fine particles 21.

(Solvent replacement step S4)
And as solvent substitution process S4, the gel fine particle 21 was wash | cleaned 5 times with acetone by the suction filtration method, and the gel fine particle 21 by which the solvent substitution was carried out was obtained.

(Supercritical drying step S5)
Further, in the supercritical drying step S5, the solvent-substituted gel fine particles 21 are placed in a stainless steel pressure vessel, CO ₂ is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then the CO ₂ is slowly added. By discharging ₂ , CO ₂ was transferred to gas phase conditions and supercritical drying was performed to obtain a gel dry powder.

(Pyrolysis step S6)
Finally, as the pyrolysis step S6, the gel dry powder was put in an electric furnace, heated at 1000 ° C. for 4 hours in a nitrogen atmosphere, and then cooled. Thus, a powdery carbon aerogel was obtained.

  About the manufacturing method of Examples 1-3 which is such a procedure, it was evaluated whether the effect of this invention could be exhibited. Specifically, the particle size distribution of the gel fine particles 21 of Examples 1 to 3 obtained in the above-described film emulsification step S2 was measured by a laser diffraction method.

  FIGS. 5-7 is a graph which shows the particle size distribution of the gel fine particle 21 of Examples 1-3.

  As shown in FIG. 5, the gel fine particles 21 of Example 1 have a very small average particle diameter of about 3 μm and a particle diameter within a very narrow specific range (standard deviation value: 0. 0). 148). In particular, the average particle diameter is about three times the pore diameter of 1 μm of the SPG film 13, which is a favorable result according to empirical rules.

  Further, as shown in FIG. 6, the gel fine particles 21 of Example 2 have an average particle diameter as small as about 7 μm, and the particle diameter is within a specific range narrow to some extent.

  Here, as shown in Table 1, Example 1 only has a longer polymerization time before membrane emulsification than Example 2. From this, in the membrane emulsification step S2, by allowing a certain amount of pre-emulsification polymerization time to pass, crosslinking with formaldehyde proceeds to a desirable degree, and the dispersion has a characteristic that facilitates good membrane emulsification. Conceivable.

  Moreover, since both Example 1 and Example 2 use the amount of surfactant as very small as 0.5 vol%, the problem that the pore characteristic of carbon airgel will change under the influence of surfactant. It is speculated that this has not occurred.

  Next, as shown in FIG. 7, the gel fine particles 21 of Example 3 exhibit a particle size distribution in which the particle diameter is bipolar in a range around 4 μm and a range around 70 μm.

  For this reason, if the amount of the surfactant used is reduced, the particle size of the gel fine particles 21 obtained by the membrane emulsification method becomes smaller and the particle size tends to fall within a narrow range to some extent. Conceivable.

  From the above results, it is clear that the manufacturing methods of Examples 1 to 3 can achieve the effects as follows.

  That is, in the production methods of Examples 1 to 3, organic wet sols are emulsified by membrane emulsification to form sol fine particles, and the sol fine particles are polymerized to form gel fine particles. Conventional pulverization after pyrolysis It does not have a process. For this reason, in the manufacturing method of Examples 1-3, the carbon airgel maintained as it is can be obtained, without destroying the pore structure of the gel microparticles 21 obtained by the membrane emulsification method.

  Moreover, since the gel fine particles 21 obtained by the production methods of Examples 1 to 3 pass through the pores of the SPG film 13, the particle diameter can be selected by selecting and controlling the pores 13b of the SPG film 13. Can be made fine, and the variation in particle diameter can also be reduced.

  In particular, in Examples 1 to 3, since the pore diameter of the SPG film 13 is uniform at about 1 μm, the obtained gel fine particles 21 are also monodisperse particles having a uniform particle diameter of about 3 μm. For this reason, the pulverized carbon airgel obtained by the sol fine particles 21 undergoing the polymerization step S3, the solvent replacement step S4, the supercritical drying step S5, and the thermal decomposition step S6 is similarly fine particles within a specific range. It has a diameter. For this reason, it is not necessary to classify the obtained carbon aerogel, and the yield can be greatly improved.

  Moreover, the manufacturing method of Examples 1-3 can reduce the usage-amount of surfactant significantly, or it can be made not to use at all by adopting a membrane emulsification method. For this reason, the problem that the pore characteristics of the carbon airgel change due to the large amount of the surfactant used can be prevented.

Therefore, the production methods of Examples 1 to 3 can provide carbon airgel having the fine pore diameter in a specific range while maintaining the pore characteristics in the production process.
.

  In the above, the present invention has been described with reference to the first to third embodiments. However, the present invention is not limited to the first to third embodiments, and can be appropriately modified and applied without departing from the spirit of the present invention. Needless to say.

  The carbon aerogel according to the present invention can be used for catalyst carriers such as fuel cells, electrode materials such as capacitors, adsorbents, column packing materials, and the like.

2 is a process diagram illustrating a method for producing a carbon airgel of Example 1. FIG. It is a schematic diagram of an SPG membrane emulsification device. It is a principal part expanded sectional view of a SPG film | membrane. It is a graph which shows an example of the pore distribution of a SPG membrane. 3 is a graph showing the particle size distribution of gel fine particles of Example 1. 6 is a graph showing the particle size distribution of gel fine particles of Example 2. 6 is a graph showing the particle size distribution of gel fine particles of Example 3. It is process drawing which shows the manufacturing method of the conventional carbon airgel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... SPG membrane emulsification apparatus 13 ... SPG membrane 20 ... Dispersed phase liquid 21 ... Fine particle 30 ... Continuous phase liquid S1 ... Sol adjustment process S2 ... Membrane emulsification process S3 ... Polymerization process S4 ... Solvent substitution process S5 ... Supercritical drying process S6 ... Thermal decomposition process

Claims (7)

A first step of obtaining an organic wet solubilized product,
A second step of emulsifying the organic wet solubilized product by a membrane emulsification method into sol fine particles;
A third step of polymerizing the sol fine particles to form gel fine particles;
A fourth step in which the gel fine particles are contacted with a water-soluble organic solvent to perform solvent substitution;
A fifth step of supercritical drying the solvent-substituted gel fine particles to obtain a gel dry powder;
And a sixth step of pyrolyzing the gel dry powder to form a carbon aerogel.   The method for producing a carbon aerogel according to claim 1, wherein the membrane emulsification method is an SPG membrane emulsification method.   The method for producing a carbon aerogel according to claim 1 or 2, wherein the gel fine particles are obtained by polymerizing polyhydroxybenzene and formaldehyde in the presence of a base catalyst.   The method for producing a carbon airgel according to claim 3, wherein the polyhydroxybenzene is dihydroxybenzene and / or a dihydroxybenzene derivative.   The method for producing a carbon aerogel according to claim 4, wherein the dihydroxybenzene is resorcinol.   The method for producing a carbon aerogel according to any one of claims 1 to 5, wherein the water-soluble organic solvent is one or a mixed solvent of methanol, acetone and amyl acetate.   The organic wet solubilized product was emulsified by a membrane emulsification method to form sol fine particles, the sol fine particles were polymerized to form gel fine particles, and the gel fine particles were contacted with a water-soluble organic solvent to perform solvent replacement, and then the solvent was replaced. A carbon aerogel obtained by supercritically drying the gel fine particles to obtain a gel dry powder and thermally decomposing the gel dry powder.

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