JP7088537B2 - Method for manufacturing spherical composite carbon material - Google Patents

Description

The present invention relates to a method for producing a spherical composite carbon material having a high specific surface area and excellent adsorption performance and the like.

Carbon materials with a high specific surface area have been attracting attention in recent years as one of the materials for solving global warming and energy problems. For example, applications of carbon materials such as adsorbents for adsorbing and containing CO ₂ gas, which is a cause of global warming, and electrode materials for power storage devices for storing electric energy obtained from solar power generation. Is diverse. In either case, the fine structure of the pores of the carbon material having a high specific surface area plays an important role, and the micropores are suitable for adsorbing CO ₂ gas, and the application of the power storage device. Then, it is necessary to develop not only micropores but also mesopores in order to facilitate smooth diffusion of the adsorbed substance into the pores.

The applicant has been developing a carbon material using phenol resin, which is one of the thermosetting resins, as a carbon precursor. Phenol resin is a material with high carbonization yield, few impurities, and high purity. It is a carbon material because it retains its original shape even after carbonization and it is easy to control its microstructure. It is an excellent carbon precursor (see, for example, Patent Documents 1 to 4).

Japanese Patent No. 5246728 Japanese Patent No. 5246729 Japanese Patent No. 5536384 Japanese Patent No. 5829456

As described above, a carbon material having excellent properties can be obtained by using a phenol resin as a carbon precursor and heat-treating it and firing it, but daily efforts are made to further improve the adsorption capacity such as gas adsorption capacity. The current situation is that they are required to do so.

Further, depending on the use and usability of the carbon material, it may be desired to have the form of spherical particles as the carbon material.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for producing a spherical composite carbon material having further improved adsorption capacity such as gas adsorption capacity.

In the method for producing a spherical composite carbon material according to the present invention, phenols and aldehydes are mixed with cellulose nanofibers and a dispersant and reacted in the presence of a reaction catalyst into spherical particles of phenol resin. A spherical composite material containing cellulose nanofibers was prepared, and the reaction was continued until the phenol resin produced by the above reaction became insoluble and infusible, and the spherical composite material thus obtained was fired. It is characterized by being carbonized and activated. The spherical composite carbon material thus obtained is formed by containing the activated carbonized product of cellulose nanofibers in the spherical particles made of the activated carbonized material of the phenol resin.

The carbonized product of the activated phenolic resin develops relatively large pores mainly corresponding to mesopores, and the carbonized product of activated cellulose nanofibers develops smaller pores mainly corresponding to micropores. , A composite carbon material having a higher specific surface area than a carbonized product activated by activating a phenol resin alone as a carbon precursor can be obtained, and the adsorption capacity such as gas adsorption capacity can be further improved. Moreover, since the composite carbon material is spherical particles, it has excellent fluidity and is highly convenient to handle such as weighing work and compounding work, and it is also used as a filler and as a medicinal adsorbent to be taken orally. It can be used for various purposes.

According to the above-mentioned production method according to the present invention, it is possible to obtain a spherical composite material containing cellulose nanofibers in spherical particles of phenol resin only by the step of mixing phenols, aldehydes and cellulose nanofibers. It is possible, and by calcining and activating this spherical composite material, the pores formed in the carbonized product of the phenolic resin and the pores formed in the carbonized product of the cellulose nanofibers are distributed. A spherical composite carbon material having a structure can be obtained, and the surface of the carbonized product of the phenolic resin is formed at the place where the cellulose nanofibers, which are more easily thermally decomposed at a lower temperature than the phenolic resin and have a low carbonization yield, disappear during firing. A spherical composite carbon material having a high specific surface area can be obtained by forming macroscopic pores.

Further, the present invention is characterized in that, in producing the composite carbon material as described above, KOH is used as an activator to perform the activation firing treatment.

By firing with KOH mixed as an activator, the pores formed in the carbonized product of phenol resin or cellulose nanofibers can be micronized to develop the pore structure, and the specific surface area can be developed. Is the one that can obtain a higher composite carbon material. Moreover, when KOH is used as the activator, carbonization and activation can be promoted at the same time for firing treatment in one step, and a composite carbon material can be obtained in a process-saving and energy-saving manner.

The composite carbon material produced by the present invention has a microstructure in which pores corresponding to mesopores and micropores formed in a carbonized product of a phenol resin or a carbonized product of cellulose nanofibers are distributed, and is phenol. It is possible to obtain a composite carbon material having a higher specific surface area than a carbonized product of a resin alone, and to obtain a composite carbon material having further improved adsorption capacity such as gas adsorption capacity. Moreover, since the composite carbon material is spherical particles, it is highly convenient to handle due to its excellent fluidity, and can be applied to various applications such as as a filler and as a medicinal adsorbent to be taken. Is what becomes.

Further, according to the method for producing a spherical composite carbon material according to the present invention, a spherical composite material containing cellulose nanofibers in spherical particles of a phenol resin can be obtained only by the step of mixing phenols, aldehydes and cellulose nanofibers. It can be obtained, and by calcining and activating this spherical composite material, the pores formed in the carbonized product of the phenolic resin and the pores formed in the carbonized product of the cellulose nanofibers are distributed. A spherical composite carbon material having a structure can be obtained. Moreover, since macropores are formed on the surface of the carbonized product of the phenol resin at the portion where the cellulose nanofibers disappear during firing, a spherical composite carbon material having a high specific surface area can be obtained.

Further, by performing the activation treatment using KOH as an activator, the pores formed in the carbonized product of the phenol resin or the cellulose nanofiber can be micronized to develop the pore structure, and the specific surface area is higher. A spherical composite carbon material can be obtained.

Hereinafter, embodiments of the present invention will be described.

The carbon precursor of the spherical composite carbon material according to the present invention is mainly composed of a phenol resin and cellulose nanofibers.

Phenol resins are obtained by reacting phenols and aldehydes in the presence of a reaction catalyst. Phenols mean phenol and derivatives of phenol, for example, in addition to phenol, trifunctional ones such as m-cresol, resorcinol, 3,5-xylenol, and tetrafunctional ones such as bisphenol A and dihydroxydiphenylmethane. Bifunctional o- or p, such as, o-cresol, p-cresol, p-ter-butylphenol, p-phenylphenol, p-cumylphenol, p-nonylphenol, 2,4 or 2,6-xylenol. -Substituted phenols can be mentioned, and halogenated phenols substituted with chlorine or bromine can also be used. Of course, in addition to selecting and using one of these, a plurality of types can be mixed and used.

As the aldehydes, in addition to formalin in the form of an aqueous solution of formaldehyde, those in the form of paraformaldehyde, acetaldehyde, benzaldehyde, trioxane, tetraoxane can also be used, and a part of formaldehyde is 2-flualdehyde. It is also possible to replace it with or full frill alcohol.

Further, as a reaction catalyst, a basic substance such as hexamethylenetetramine, ammonia, methylamine, dimethylamine, which reacts phenols with aldehydes to form a = NCH ₂ -bond between benzene nuclei and benzene nuclei, is used. Primary and secondary amines such as ethylenediamine and monoethanolamine can be used. Also, alkali metal oxides such as sodium, potassium and lithium, hydroxides and carbonates, or alkaline earth metal oxides such as calcium, magnesium and barium, hydroxides, carbonates, and tertiary amine compounds can be used. You can also list it. Specific examples of these include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, calcium hydroxide, magnesium hydroxide, barium hydroxide, calcium carbonate, magnesium oxide, calcium oxide, trimethylamine, triethylamine, and triethanol. There are amines, 1,8-diazabicyclo [5,4,0] undecene-7 and the like.

The cellulose nanofiber (CNF) used in the present invention is an ultrafine plant fiber having a diameter of 4 to 100 nm and a length of 5 to 100 μm and having a high aspect ratio, and the cellulose fiber is treated by mechanical defibration or the like. Obtained by loosening to nano size. Cellulose nanofibers have a large specific surface area and have a feature that they are easily pyrolyzed at a low temperature to become porous. In addition, it can be said that it is a renewable material derived from plants, a sustainable resource, and has a small environmental load.

Then, the above-mentioned phenols, aldehydes, and a reaction catalyst are placed in a reaction vessel such as a reaction vessel, and the phenols and the aldehydes are subjected to a condensation condensation reaction. The dispersant is put into the reaction vessel, and if necessary, an additive such as a coupling agent is put into the reaction vessel, and the reaction between the phenols and the aldehydes is carried out in the presence of these. Here, the blending amount of the aldehydes with respect to the phenols is not particularly limited, but the range of 1.0 to 3.0 mol of the aldehydes is preferable with respect to 1 mol of the phenols. The blending amount of the reaction catalyst varies greatly depending on the type of the reaction catalyst, but is preferably set in the range of 0.05 to 10% by mass with respect to the phenols.

The above dispersant used in the present invention also acts as a kind of emulsifier, for example, arabic rubber, polyvinyl alcohol, glue, guar rubber, gutte gum, carboxymethyl cellulose, hydroxyethyl cellulose, solubilized starch, agar, sodium alginate. And so on, and one of these can be used alone or in combination of two or more. Among these, gum arabic and polyvinyl alcohol can be preferably used. The amount of the dispersant added varies greatly depending on the emulsifying effect of the dispersant and is not particularly limited, but is preferably set in the range of 0.1 to 10.0% by mass with respect to the phenols. The range of 0.5 to 7.0% by mass is more preferable.

The above reaction is carried out while stirring in a liquid such as water in an amount sufficient to stir the reaction system. At the beginning of the reaction, the cellulose nanofibers may be floating on the liquid surface, but phenols and the like. As the condensation reaction between the aldehydes and the aldehydes progresses, they come into contact with the highly wet phenols and are incorporated into the liquid. As the addition condensation reaction proceeds further, the condensation reaction product of phenols and aldehydes begins to separate from the water in the system while embracing the cellulose nanofibers. The phenol resin produced by the condensation reaction of phenols and aldehydes aggregates to form a sphere due to the action of the emulsifier, and the spherical particles of the phenol resin mixed with cellulose nanofibers are dispersed in the liquid of the reaction system. It can be obtained in a state of being. Cellulose nanofibers are not mechanically mixed with phenol resin, but phenols and aldehydes undergo a condensation reaction while embracing the cellulose nanofibers to prepare spherical particles of the phenol resin that incorporate the cellulose nanofibers inside. It is possible to obtain spherical particles of a phenol resin in which cellulose nanofibers are less likely to be entangled with each other and the cellulose nanofibers are mixed in a uniformly dispersed state. When the reaction is further promoted to a desired degree and the stirring is stopped after cooling, the spherical particles are precipitated and separated from water. These spherical particles are fine water-containing particles and can be easily separated from water by filtration. By drying the spherical particles, the phenol resin can be used as free-flowing spherical particles. It is possible to obtain a spherical composite material in which cellulose nanofibers are uniformly contained in spherical particles.

Since the spherical composite material of the phenol resin and the cellulose nanofibers obtained as described above is formed of the phenol resin mixed with the cellulose nanofibers, the ratio of the cellulose nanofibers and the phenol resin is the same in each spherical composite material. Is. Therefore, it is possible to obtain a spherical composite material in which cellulose nanofibers and phenol resin are uniformly contained. Here, since the cellulose nanofibers are not mechanically mixed with the phenol resin, the blending amount of the cellulose nanofibers can be arbitrarily set, but 10 to 100 parts by mass with respect to 100 parts by mass of the phenol resin. It is preferable to set the blending amount of the cellulose nanofibers so as to be within the range.

In preparing the spherical composite material of the phenol resin and the cellulose nanofibers as described above, the addition condensation reaction between the phenols and the aldehydes was continued until the produced phenol resin became insoluble and infusible, and then stopped. By allowing the phenol resin to be completely cured, particles of a spherical composite material can be obtained. Alternatively, the addition condensation reaction between phenols and aldehydes is stopped in a state where the produced phenol resin has thermocurability, so that a spherical composite material composed of uncured phenol resin and cellulose nanofibers is prepared. If this is the case, then heating is performed to cure the phenol resin until it becomes insoluble and infusible, whereby particles of the spherical composite material in a completely cured state of the phenol resin can be obtained. The particle size of the spherical composite material is arbitrarily set according to the intended use, and is not particularly limited, but is generally about 0.001 to 0.1 mm.

Further, as described above, a spherical composite material of phenol resin and cellulose nanofibers is produced by subjecting phenols and aldehydes to a condensation condensation reaction in the presence of a reaction catalyst while mixing them with cellulose nanofibers and a dispersant. In order to carry out the reaction, the cellulose nanofibers can be put into the reaction system from the start of the addition condensation reaction. Further, the cellulose nanofibers may not be added to the reaction system at the time of starting the addition-condensation reaction of phenols and aldehydes, and the cellulose nanofibers may be added to the reaction system during the addition-condensation reaction. .. Further, it is also possible to charge the cellulose nanofibers into the reaction system in a plurality of times from the start to the end of the addition condensation reaction of phenols and aldehydes.

The present invention is made by using the above-mentioned spherical composite material of phenol resin and cellulose nanofiber as a carbon precursor, heating and firing in an atmosphere where oxygen is blocked to carbonize the phenol resin and cellulose nanofiber, and further activating them. Such a spherical composite carbon material can be obtained. Here, a spherical composite carbon material may be obtained by a two-step calcination treatment in which a calcination treatment for carbonization is performed and then a calcination treatment for activating the carbonized product is performed, or carbonization is performed by a one-step calcination treatment. And activation may proceed at the same time to obtain a spherical composite carbon material.

The activation can be carried out by a gas activation method using an activation gas such as steam or carbon dioxide, but in the present invention, it is preferably carried out by a chemical activation method using potassium hydroxide (KOH) as an activator. When the carbon precursor is calcined using KOH as an activator, carbonization and activation can proceed at the same time to treat the carbon precursor in one step. Then, by using KOH as the activator in this way, it is possible to obtain a composite carbon material in which the mesopores of the pores are developed and the specific surface area is further increased.

When KOH is used as an activator, when carbonizing and activating in a one-step firing treatment to obtain a spherical composite carbon material, it is necessary to mix KOH with the spherical composite material of phenol resin and cellulose nanofibers before the firing treatment. There is. At this time, after preparing a spherical composite material of phenol resin and cellulose nanofibers as described above, KOH can be mixed with the spherical composite material. Alternatively, by adding KOH powder to the reaction system when the phenols and aldehydes are condensed and reacted as described above, KOH can be mixed with the spherical composite material of the phenol resin and the cellulose nanofibers. Further, after the spherical composite material of the phenol resin and the cellulose nanofibers is calcined and carbonized, KOH is mixed with the carbon material of the spherical composite material and further calcined to activate the spherical composite carbon according to the present invention. You may try to get the material.

The amount of KOH added as an activator is not particularly limited, but is 50 with respect to a total of 100 parts by mass (solid content) of the phenol resin and the cellulose nanofibers in the spherical composite material of the phenol resin and the cellulose nanofibers. It is preferably set to be in the range of up to 600 parts by mass, and more preferably in the range of 100 to 400 parts by mass.

As described above, a carbon precursor made of a spherical composite material of phenol resin and cellulose nanofibers is calcined and carbonized and activated to obtain a spherical composite carbon material that can be used as activated carbon. In this spherical composite carbon material, relatively large pores mainly corresponding to mesopores are developed in the carbonized product of the activated phenol resin, and the carbonized material of the activated cellulose nanofibers mainly corresponds to the micropores. Smaller pores develop. Moreover, since the cellulose nanofibers are more easily pyrolyzed at a lower temperature than the phenol resin and the carbonization yield is low, the cellulose nanofibers disappear during firing, and the phenol resin is lost at the place where the cellulose nanofibers disappear. Macropores are formed on the surface of the carbonized product. Therefore, it is possible to obtain a spherical composite carbon material having a higher specific surface area than a carbonized product activated by activating phenol resin alone as a carbon precursor, and it is possible to further improve the adsorption capacity such as gas adsorption capacity. be.

Therefore, this spherical composite carbon material can be used as a carbon material for forming an electrode of a secondary battery such as a dry battery, a lead storage battery, or a lithium ion secondary battery. When manufacturing an electrode using a spherical composite carbon material as a carbon material for an electrode, for example, the spherical composite carbon material is dispersed in a solvent or the like together with a binder to form a slurry, and this slurry is applied to a metal foil such as a copper foil. It can be carried out by drying and press-molding. Further, this electrode can be used as a polarizable electrode to form an electric double layer capacitor that forms an electric double layer formed at the interface of the electrolytic solution. As described above, by manufacturing the electrode for the secondary battery and the electric double layer capacitor polarized electrode using the spherical composite carbon material of the present invention, the secondary battery and the electric double layer capacitor having high charge / discharge capacity can be obtained. It is something that can be done.

This spherical composite carbon material can also be used for water purification or the like due to its high adsorptive action. In addition, if the harmful substance to be adsorbed is not rapidly adsorbed in the digestive tract, the harmful substance is absorbed into the body. Therefore, an adsorbent having a high adsorption rate is required. However, the spherical composite carbon material has a unit mass by activation treatment. Since the specific surface area per contact and the pore volume are increased to improve the physical and chemical adsorption performance, this can be used as a medicinal oral adsorption carbon agent. For example, it can be used as a therapeutic agent for chronic renal failure, a therapeutic agent for gastrointestinal diseases such as Crohn's disease, and a therapeutic agent for ulcerative colitis and irritable bowel syndrome.

Next, the present invention will be specifically described with reference to Examples.

(Example 1)
200 g of phenol, 80 g of 25% cellulose nanofiber paste, and 200 g of tap water were placed in a 2 L four-necked flask and stirred at room temperature for 30 minutes. The 25% cellulose nanofiber paste 80 g is composed of 20 g of cellulose nanofibers and 60 g of water, so that the mass ratio of phenol to cellulose nanofibers is 100:10. Next, 104 g of 92% paraformaldehyde, 26 g of hexamethylenetetramine, 2 g of Arabic rubber and 1300 g of tap water were put into this flask, and the temperature inside the flask was raised to 100 ° C. while continuing stirring, and then 100 ° C. The reaction was carried out at temperature for 3 hours.

Next, after cooling the inside of the flask, the contents of the flask are filtered, washed with water, and then dried to obtain a spherical composite material in which cellulose nanofibers are uniformly contained in the spherical particles of the phenol resin. rice field. This spherical composite material was true spherical particles having a particle size in the range of 0.001 to 0.1 mm, and the phenol resin was cured in an insoluble and infusible state.

200 g of a spherical composite material of phenol resin and cellulose nanofibers obtained as described above was placed in a crucible to cover it, and the crucible was further placed in a heat-resistant container to fill the gap with coke. Then, this was placed in a heating furnace, heated to 800 ° C. at a heating rate of 10 ° C./min, and fired at a heating temperature of 800 ° C. for 2 hours to carry out carbonization treatment and activation treatment. .. The mass of the spherical composite carbon material thus obtained was 70 g, and the yield after firing was 35% by mass.

(Comparative Example 1)
200 g of phenol and 200 g of tap water were placed in a 2 L four-necked flask and stirred at room temperature for 30 minutes. Next, 104 g of 92% paraformaldehyde, 26 g of hexamethylenetetramine, 2 g of Arabic rubber and 1300 g of tap water were put into this flask, and the temperature inside the flask was raised to 100 ° C. while continuing stirring, and then 100 ° C. The reaction was carried out at temperature for 3 hours.

Next, after cooling the inside of the flask, the contents of the flask were filtered, washed with water, and then dried to obtain spherical particles of phenol resin. The spherical particles were true spherical particles having a particle size in the range of 0.001 to 0.1 mm, and the phenol resin was cured in an insoluble and infusible state. Then, using 200 g of the phenolic resin spherical particles, a spherical carbon material was obtained by firing in the same manner as in Example 1, then washing and drying. The mass of this spherical carbon material was 100 g, and the yield after firing was 50% by mass.

Nitrogen adsorption measurement was performed on the spherical carbon materials of Example 1 and Comparative Example 1 obtained as described above, and the specific surface area, the total pore volume, the micropore volume, and the mesopore volume were calculated. Here, the nitrogen adsorption measurement was carried out using "Belsorp-Max II" manufactured by Microtrac Bell Co., Ltd. under a temperature condition of -196 ° C. The sample used for the nitrogen adsorption measurement was dried while degassing at 300 ° C. for 3 hours before the measurement, and the water adhering to the sample was completely removed.

The specific surface area was calculated from the nitrogen adsorption isotherm obtained by the nitrogen adsorption measurement based on the Brunauer-Emmet-Teller (BET) method. The total pore volume was calculated from the amount of nitrogen adsorbed at a relative pressure of 0.99 on the nitrogen adsorption isotherm. The micropore volume was calculated based on the t-plot method. The mesopore volume was calculated based on the Barrett-Joyner-Halenda (BJH) method. All analyzes were performed using BELMaster (registered trademark of Microtrac Bell Co., Ltd.), which is an analysis software for specific surface area and pore volume. The results are shown in Table 1.

As can be seen in Table 1, the specific surface area and the micropore volume of Example 1 are larger than those of Comparative Example 1. It is considered that this is because the cellulose nanofibers contained in the phenol resin disappear by the heat treatment, so that the voids of the composite carbonized product are increased. As a result, the gas adsorption performance was improved by the composite of the phenol resin and the cellulose nanofibers.

(Example 2)
200 g of a spherical composite material of phenol resin and cellulose nanofibers obtained in the same manner as in Example 1 was placed in a crucible and covered, and the crucible was further placed in a heat-resistant container to fill the gap with coke. Then, this was placed in a heating furnace, heated to 800 ° C. at a heating rate of 10 ° C./min, and fired at a heating temperature of 800 ° C. for 1 hour to carry out carbonization treatment.

Next, KOH was mixed with the spherical composite material carbonized by carbonization as described above in a mass ratio of 1: 1. Here, KOH was used in a state where 50 parts by mass was dispersed with respect to 100 parts by mass of water, and after mixing the dispersed water of KOH with the carbonized spherical composite material, it was dried at 120 ° C. for 15 hours. Then, the mixture of the carbonized spherical composite material and KOH was put in a crucible and covered, and the crucible was further put in a heat-resistant container and the gap was filled with coke. Next, this was placed in a heating furnace, heated to 800 ° C. at a heating rate of 10 ° C./min, and fired at a heating temperature of 800 ° C. for 1 hour to perform activation treatment.

After cooling to room temperature, the obtained carbonized product was taken out, neutralized with an aqueous solution of HCL having a concentration of 1 mol / L, and further washed with distilled water 5 times to remove the residual potassium mixture. Then, it was dried at 120 ° C. for 15 hours to obtain a spherical composite carbon material. The mass of this spherical composite carbon material was 50 g, and the yield after firing was 25% by mass.

(Comparative Example 2)
Using 200 g of spherical particles of phenol resin obtained in the same manner as in Comparative Example 1, firing was carried out in the same manner as in Example 2 for carbonization treatment. Next, KOH was mixed with this carbonized product and calcined in the same manner as in Example 2 to activate the spherical carbon material. The mass of this spherical carbon material was 75 g, and the yield after firing was 30% by mass.

With respect to the spherical carbon materials of Example 2 and Comparative Example 2 obtained as described above, nitrogen adsorption measurement was performed in the same manner as described above, and the specific surface area, the total pore volume, the micropore volume, and the mesopore volume were calculated. The results are shown in Table 2.

As can be seen in Table 2, when Example 2 and Comparative Example 2 are compared, the specific surface area and the micropore volume are increased in Example 2. This is because a more porous carbon material can be obtained and gas adsorption characteristics are improved by adding cellulose nanofibers and activating with KOH rather than directly activating the carbonized product of the phenol resin with KOH. It is shown that. It is expected that a high specific surface area and porous carbon can be prepared by the synergistic effect of the activation effect of KOH and the decomposition of cellulose nanofibers.

Claims (2)

By reacting phenols and aldehydes with cellulose nanofibers and a dispersant in the presence of a reaction catalyst, a spherical composite material containing cellulose nanofibers in the spherical particles of the phenol resin is prepared . At the same time, the reaction is continued until the phenolic resin produced by the above reaction becomes insoluble and infusible , and the spherical composite material thus obtained is calcined and activated by firing treatment. How to make the material. The method for producing a spherical composite carbon material according to claim 1 , wherein the activation firing treatment is performed using KOH as an activator.