JPS6353154B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention produces a porous phenol/polyvinyl acetal synthetic resin body with continuous pores obtained by mixing a phenol resin and polyvinyl alcohol with a pore-forming material and curing the mixture in the presence of a crosslinking agent in a non-oxidizing atmosphere. The present invention relates to a method for producing a porous carbon body having continuous pores which is at least partially made of glassy carbon. Conventionally, the method for producing porous carbon bodies has been to mix amorphous or spherical carbon or graphite with resin, tar, or pitch, and then mold and sinter the mixture. (JP-A-48-67188, etc.) However, the carbon porous bodies produced by these methods have a relatively large apparent specific gravity (1.00 to 1.30) and therefore a small porosity. In addition, a method for manufacturing porous bodies (Japanese Patent Publication No. 1999-1999) has been proposed in which carbonaceous micro hollow bodies are molded using a binder and then fired; however, although this method has a relatively small apparent specific gravity ( 0.05-1.00), most of the pores are independent pores, and the air permeability is extremely small. Furthermore, a method for manufacturing a carbon porous body (Japanese Patent Publication No. 49-26196, etc.) has been proposed in which a thermosetting resin is attached to a fibrous structure, followed by molding and firing. It has been difficult to freely control the porosity to a desired size and to produce a carbon porous body having continuous pores with a narrow pore size distribution. In order to improve the shortcomings of these conventional manufacturing methods for carbon porous bodies and to produce porous bodies with large porosity and continuous pores, we impregnated and hardened polyurethane foam with a resin that can be converted into glassy carbon when heated. A method has been proposed in which carbonization is then carried out at a high temperature. U.S. Pat. No. 3,922,334 discloses that an open-pore network polyurethane structure obtained by removing the thin partition walls of a polyurethane foam is infiltrated with a phenolic resin solution using tetrahydrofuran as a solvent, and then over a relatively long period of time. A carbon porous body that is carbonized and fired so that the skeleton of the network-like polyurethane structure of the base material becomes the carbon skeleton is disclosed. Further, US Pat. No. 3,927,186 discloses a carbon porous body that utilizes the skeleton of a network polyurethane structure by impregnating the network polyurethane structure with a liquid furan resin and carbonizing it. Although the methods using polyurethane foams described in these US patents are excellent, great care is required to remove excessively permeated resin from the surface of the polyurethane after resin impregnation. Also, depending on the solvent, when polyurethane foam is impregnated with resin, the resin begins to dissolve the foam.
Foams may collapse during heat curing, and this tendency is particularly noticeable in flexible polyurethane foams. For this reason, JP-A-51-70207 introduces a complicated process of impregnating a polyurethane foam with a liquid epoxide resin or an aqueous polyvinyl alcohol solution prior to resin impregnation. Furthermore, JP-A-53-125289 discloses that a flexing gas is introduced into a thermosetting resin foam obtained by directly reacting a mixture of a polyisocyanate and a phenol resin or a furan resin or a precursor thereof. However, a method for manufacturing a porous carbon material having continuous pores by igniting a flexible gas to destroy cell membranes and then performing carbonization firing has been disclosed, but this method has the drawback that the manufacturing process is complicated. ing. Polyurethane foam is originally a closed-cell foam, and to obtain a network structure with completely open pores, special treatment must be performed to remove the pore partition walls in advance, or a similar treatment must be performed after resin impregnation. shall be. As mentioned above, although the carbon porous body using polyurethane foam has excellent properties, it has the disadvantage that the manufacturing method is complicated. By the way, the polyvinyl acetal porous material is
In addition to polyvinyl alcohol and aldehydes as a crosslinking agent, starch, water-soluble salts, etc. are mixed and crosslinked.
This is a porous body in which continuous pores are imparted by eluting water-soluble substances with water after solidification, and it is a hydrophilic porous body with extremely high continuous porosity. As a method for producing a carbon porous body that takes advantage of the excellent properties of the porous body, a method has been proposed in which the porous body is carbonized and fired in a non-oxidizing atmosphere. (Special request 1973)
-70069) However, when the above polyvinyl acetal porous material is carbonized and fired in a non-oxidizing atmosphere, the weight loss during firing is extremely large.
In addition, the size is significantly reduced and non-uniform deformation occurs during shrinkage, which is a serious drawback. Furthermore, since the porous body is made of easily graphitizable carbon, it has drawbacks such as poor oxidation resistance and chemical resistance. The present inventors have completed the present invention as a result of intensive research to improve the above-mentioned drawbacks found in existing methods for producing porous carbon materials. The object of the present invention is to provide a new method for producing a porous carbon material having a high porosity. Other objects and advantages of the invention will become apparent from the description below. The above purpose is to create a phenol/polyvinyl acetal system with continuous pores obtained by mixing phenolic resin and polyvinyl alcohol with a pore-forming material, reacting and curing the mixture in the presence of a cross-linking agent, and then washing and removing the pore-forming material. This is achieved by firing the synthetic resin porous body in a non-oxidizing atmosphere. The phenol/polyvinyl acetal-based synthetic resin porous body of the present invention is cross-linked by mixing starch, water-soluble salts, etc. in addition to phenol resin, polyvinyl alcohol, and aldehydes as cross-linking agents, and after solidification, water-soluble substances are It can be manufactured by eluating with water to provide continuous pores. A water-soluble resol resin is suitable as the phenol resin used for producing this phenol/polyvinyl acetal synthetic resin porous body. Resol resins are initial products produced by reacting phenols with aldehydes in the presence of a basic catalyst, and are generally
A water-soluble resol can be obtained by keeping an initial condensate obtained by reacting 1.5 to 3.5 moles of aldehydes in the presence of a slightly excess alkaline catalyst in a stable water-soluble state. Phenols used in the production of resol resins most commonly include phenols and cresols. However, other phenols can also be used, such as phenol, O-cresol, m-cresol, p-cresol, 2,3-xylenol,
2,5-xylenol, 2,4-xylenol,
2,6-xylenol, 3,4-xylenol,
3,5-xylenol, 0-ethylphenol,
m-ethylphenol, p-ethylphenol,
Examples include p-phenylphenol, p-tert-butylphenol, p-tert-aminophenol, bisphenol A, resorcinol, and mixtures of these phenols. Formaldehyde is the most common aldehyde used for polycondensation with this phenol. However, monoaldehydes and dialdehydes such as paraformaldehyde, hexamethylenetetramine, furfural and glutaraldehyde, azibaldehyde and gluoxal may also be used. As the basic catalyst used in the resol resin synthesis reaction, known catalysts such as caustic alkali, alkali carbonate, barium hydroxide, calcium hydroxide, ammonia, quaternary ammonium compounds, and amines may be used. is most commonly used. Further, the polyvinyl alcohol used for producing the phenol/polyvinyl acetal synthetic resin porous body of the present invention preferably has a degree of polymerization of 100 to 5000 and a degree of saponification of 70% or more, and may also be partially modified with carboxyl groups or the like. Suitably used. Examples of aldehydes used as crosslinking agents include formaldehyde, acetaldehyde, propionaldehyde, o-butyraldehyde, octylaldehyde, 2-ethylhexylaldehyde, glyoxal, acrolein, and benzaldehyde. As the pore-forming material for providing continuous pores, starch, other organic fine powders, water-soluble metal salts, etc. can be used. The type and size of the powder may be appropriately selected depending on the pore diameter of the intended porous body. To produce a phenol/polyvinyl acetal synthetic resin porous body using the above-mentioned phenolic resin, polyvinyl alcohol, and pore-forming material, first, a predetermined amount of a mixed aqueous solution of phenolic resin and polyvinyl alcohol is heated while stirring, and then A pore-forming material such as wheat flour starch in an aqueous solution or aqueous dispersion is added to this mixture, and the mixture is further stirred. After cooling to about 40°C, aldehydes as a crosslinking agent and sulfuric acid as a catalyst are added and mixed uniformly. Then, it is transferred to a mold of the desired shape and heated to cause a reaction. In addition to sulfuric acid, catalysts include inorganic acids such as hydrochloric acid and phosphoric acid, oxalic acid, formic acid, acetic acid, propionic acid,
Organic acids such as butyric acid, lactic acid, maleic acid, malonic acid, vinyl acetic acid, para-toluenesulfonic acid, and benzenesulfonic acid can be used. After the reaction is completed, the molded product taken out from the mold is washed with water to wash away the aldehydes and acid that have not reacted with the pore-forming material. The shape of the molded product can be freely selected, such as a plate shape or a wavy cylindrical shape, depending on the purpose, use, and required performance. The content of phenolic resin in the phenol/polyvinyl acetal synthetic resin porous body prepared by the above method is usually 10 to 85% by weight, preferably
30-80% by weight, most preferably 40-75% by weight. If the content of phenolic resin in the synthetic resin porous body is extremely low, the weight loss and size decrease will be large during the carbonization firing process in a non-oxidizing atmosphere, and non-uniform changes will likely occur. However, since the strength is low, problems may arise depending on the application. If the content of the phenolic resin exceeds 85% by weight, it becomes difficult to remove the pore-forming material and unreacted aldehydes and acids during washing after the curing reaction is completed, making it difficult to obtain a porous body with a large continuous porosity. becomes difficult. The content of phenolic resin in the porous body is 40
When the amount is 75% by weight, a high-strength carbon porous body with a small amount of shrinkage during carbonization firing and a high continuous porosity can be obtained. In addition, when creating the above-mentioned phenol/polyvinyl acetal synthetic resin porous body, resin powders such as phenol resin and furan resin, fibrous materials, or inorganic powders such as silica, alumina, graphite, and silicon carbide, copper, By mixing an appropriate amount of metal powder such as nickel, it is possible to suppress deformation during firing and improve shape retention without impairing the characteristics of a porous body having continuous pores. In addition to the phenol/polyvinyl acetal synthetic resin porous body obtained as described above, a mixed solution of a phenol resin such as a resol resin or a novolak resin, a furan resin, a melamine resin, an epoxy resin, a vinyl polymer and a divinyl compound, It is also possible to impregnate or adhere urea resin, unsaturated polyester resin, pitch, tar, etc. Various known methods can be applied to apply these synthetic resins, but the most common method is to apply continuous pores with a predetermined shape, size, pore diameter, and porosity manufactured by the above-mentioned method. The phenol/polyvinyl acetal-based synthetic resin porous body having the above-mentioned material may be immersed in a solution prepared by dissolving the above-mentioned synthetic resin in a solvent, and then dried and cured. The porous phenol/polyvinyl acetal synthetic resin material thus prepared is then heated under a non-oxidizing atmosphere, that is, under reduced pressure, or in an inert gas such as argon gas or helium gas, hydrogen gas, nitrogen gas, or halogen gas. at least 800℃ inside,
Preferably, it is heated to 1000°C or higher and carbonized and fired.
There is no limit to the upper limit of the firing temperature, and it can be set to 3000 as needed.
It may be heated to about ℃. According to the research of the present inventors, 200℃ during carbonization firing
From the vicinity, mainly gaseous compounds, e.g.
H ₂ O, HCHO, CO, CH ₄ , etc. begin to be released from the porous body, but the generation of this thermal decomposition gas is
It is most noticeable in the temperature range of 600°C, and weight loss and shrinkage of the resin composition proceed significantly in this temperature range. However, in the carbonization firing process of the present invention, there is no particular restriction on the temperature increase rate, and it is usually 50℃/hr ~
It is possible to bake in a relatively short time at about 500°C/hr. The carbon porous material obtained according to the above method is a reticulated carbon structure consisting at least partially of glassy carbon, in which the skeleton constituting the reticulated structure of the phenol/polyvinyl acetal synthetic resin porous material remains the carbon skeleton. This porous body has continuous pores with a uniform pore size distribution, high porosity, and excellent oxidation resistance and chemical resistance. In addition, the carbon porous body retains the network structure of the phenol/polyvinyl acetal synthetic resin porous body, and therefore has high rigidity and strength. A carbon porous body having such excellent properties is suitable for the following uses. That is, it is suitable for various types of filters, such as those used to separate solids such as dust and impurities in gases and solids in liquids, particularly filters with excellent corrosion resistance or heat resistance. In addition, it is suitable as a catalyst carrier that takes advantage of its good air permeability. Furthermore, the porous material can be used as a panel heater by making use of its conductivity and passing an electric current through the porous material. Furthermore, by performing treatments such as steam activation treatment and chemical activation treatment to activate carbonization, it can be used as activated carbon having a network structure or as an adsorbent. In addition to the above-mentioned uses, the carbon porous body can also be used for lightweight structural materials, heat insulating materials, battery electrodes, aeration devices, chemical adsorbents, surface heating elements, radio wave shielding materials, and the like. Next, the present invention will be explained in more detail with reference to Examples. Example 1 Polyvinyl alcohol with a degree of polymerization of 1700 and a degree of saponification of 99% was dispersed in water, then heated and dissolved, and when the temperature reached 60°C, an aqueous dispersion of wheat flour starch having a predetermined particle size was added and mixed uniformly. Furthermore, a specified amount of water-soluble resol (manufactured by Sumitomo Durez, RP961A) was added,
Heat to 70-80°C with stirring. This mixture
After cooling to 40℃, 37% formalin and sulfuric acid were added and mixed uniformly, 8% phenol and polyvinyl alcohol combined, 4% starch, 10% formalin.
%, a solution consisting of 10% sulfuric acid was prepared. The solution was poured into a hollow cylindrical mold with an outer diameter of 70 mmφ, an inner diameter of 30 mmφ, and a height of 300 mm, heated at 60°C for 18 hours, and then washed with water to elute starch and terminal reactants. I got a body. The average pore diameter of the porous body was 100μ. The synthetic resin porous body obtained as described above was placed in an electric furnace and heated at a rate of 150°C/hr in a nitrogen atmosphere to be carbonized and fired, maintained at 1000°C for 1 hour, and then cooled.
Table 1 shows the properties of the obtained porous carbon material. As shown in Table 1, when the phenol content was less than 10%, both the weight loss and the dimensional change were extremely large, and the resulting carbon porous body had a shape that was significantly more distorted than the cylindrical shape. In addition, the phenol content is 85
%, the continuous porosity decreases significantly,
It became difficult to remove the pore-forming material and the end reactants, and it was not possible to obtain a good porous carbon material. When the phenol content was in the range of 10 to 85% by weight, a carbon porous body with a continuous porosity of 50% or more and good shape retention during firing was obtained.

[Table] Example 2 In the same manner as in Example 1, a 10 mm thick plate-shaped phenol/polyvinylbenzal porous body was prepared by using benzaldehyde instead of formalin. The average pore diameter of the porous body was 50μ. A resol resin, a furan resin, and a melamine resin were attached to the above phenol/polyvinylbenzal porous material by the following method. That is, a commercially available molding resol resin (AP-106GK manufactured by Gunei Chemical Co., Ltd.) was used as the resol resin, and after diluting it with methanol solvent to a predetermined concentration, the above porous body was immersed, and the excess was removed using a centrifuge. After removing the solution, 150℃
and cured for 90 minutes. Further, the furan resin was immersed in frifuryl alcohol to which 2% by weight of balatoluenesulfonic acid was added as a catalyst, then taken out, and after removing excess solution with a centrifuge, it was cured at 150°C for 90 minutes. As the melamine resin, a commercially available water-soluble melamine resin (manufactured by Sumitomo Chemical, Sumitex Resin M3; curing catalyst, Sumitex ACX) was used in the same manner.
After adhering to a synthetic resin porous body, it was dried at 140°C for 2 hours. The synthetic resin porous body thus obtained was placed in an electric furnace, heated at a rate of 100° C./hr in a nitrogen atmosphere, carbonized and fired, maintained at 900° C. for 1 hour, and then cooled. Table 2 shows the properties of the obtained porous carbon material. As can be seen from Table 2, by attaching synthetic resin such as phenol resin, furan resin, melamine resin, etc. to the phenol/polyvinyl acetal resin porous body and then firing it, the weight retention rate and dimensions at the time of firing can be improved. The retention rate increases and shape retention can be improved.

【table】

[Table] Example 3 In the same manner as in Example 1, n-butyraldehyde was used instead of formalin, and phenol/
A porous polyvinyl butyral material was synthesized. The porous body was molded into a flat plate by carrying out a butyralization reaction in a mold of 20 x 200 x 200 mm. The average pore diameter of the phenol/polyvinyl butyral synthetic resin porous body was 3 μm. The synthetic resin porous body was placed in an electric furnace, heated at a rate of 300° C./hr in a nitrogen atmosphere, maintained at a predetermined temperature for 1 hour, and then cooled. The carbon porous body thus obtained was immersed in a mixed solution of concentrated nitric acid/concentrated hydrochloric acid=5/1 (volume ratio) at 80° C. for 96 hours. The results are shown in Table 3. From Table 3, when the firing temperature is 800℃ or higher,
It can be seen that the obtained porous carbon material has excellent chemical resistance.

【table】

Claims (1)

[Scope of Claims] 1. Phenol/polyvinyl having continuous pores obtained by mixing a phenolic resin and polyvinyl alcohol with a pore-forming material, reacting and curing the mixture in the presence of a cross-linking agent, and then washing and removing the pore-forming material. A method for producing a carbon porous body having continuous pores made at least partially of glassy carbon by firing an acetal-based synthetic resin porous body in a non-oxidizing atmosphere. 2. The method for producing a porous carbon material according to claim 1, wherein the phenolic resin is a water-soluble resol. 3. The method for producing a porous carbon material according to claim 1, wherein the crosslinking agent is formaldehyde or benzaldehyde. 4. The method for producing a carbon porous body according to claim 1, wherein the content of phenolic resin is 10 to 85% by weight. 5. The method for producing a carbon porous body according to claim 1, which comprises firing at 800° C. or higher in a non-oxidizing atmosphere.