JP6236322B2 - Carbide and method for producing the same - Google Patents

Description

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

  Carbides are used not only for adsorbents such as desiccants and deodorizers but also as electrode materials for power storage devices such as batteries and electric double layer capacitors. From the viewpoint of reducing impurities in carbides, it has been studied to use synthetic resins as raw materials for carbides. As the synthetic resin, a thermosetting resin such as a phenol resin is generally used. However, since thermosetting resins are expensive and have a low degree of freedom in shape, the use of thermoplastic resins, which are superior to thermosetting resins in these respects, as raw materials has also been studied.

  In particular, when a thermoplastic resin is used as a raw material, it is a technical problem to improve the yield of carbide. For this reason, when carbonizing a thermoplastic resin, it has been proposed to treat the thermoplastic resin in advance or add an additive to the thermoplastic resin. For example, in the case of carbonization by heat treatment of a polyvinyl alcohol-based resin, a technique for improving the yield of carbide by adding an infusibilizing agent such as sulfuric acid is known. It has also been proposed to improve the yield of carbides by halogen treatment. For example, Patent Document 1 discloses a method for producing a carbide by adding a metal salt that is an alkali metal salt or an alkaline earth metal salt to a polyvinyl alcohol resin, subjecting it to a halogen treatment, and further performing a heat treatment. According to Patent Document 1, the addition of the metal salt is effective in shortening the time required for the halogen treatment.

JP 2009-249238 A

  However, according to the conventional method described above, although the yield of carbide from the thermoplastic resin is improved, non-carbon components such as sulfur and halogen remain in the carbide. Non-carbon components remaining by conventional methods can affect the properties of the final product in which the carbide is used. In particular, in an electronic component typified by an electrode material of an electricity storage device, there is a possibility that electric corrosion occurs or a decomposition reaction of carbides involving the non-carbon component proceeds.

  Therefore, the present invention provides a new production method capable of improving the yield of carbide from a thermoplastic resin, in particular, the collection of carbide from a thermoplastic resin using an organic compound that can itself be a raw material for carbide. It aims at providing the manufacturing method which can improve a rate.

The present invention
A method for producing a carbide comprising a step (iv) of heating a mixture containing a condensate of citric acid or a citric acid derivative and a thermoplastic resin in a non-oxidizing atmosphere to carbonize the mixture,
I will provide a.
Note that the above process is described as “process (iv)” for the convenience of explanation to be described later, and does not mean that a three-stage pretreatment process is required before this process.

  From another aspect, the present invention provides a carbide obtained by the production method of the present invention.

  According to this invention, the yield of the carbide | carbonized_material from a thermoplastic resin can be improved using the condensate of the citric acid which is an organic compound, or a citric acid derivative.

X-ray diffraction spectrum of the carbide obtained in Example 3

  The following is an explanation of an embodiment of the present invention, and is not intended to limit the present invention to the following embodiment. For example, in the following, a manufacturing method including steps (i) to (iv) will be described. However, another embodiment of the present invention includes only step (iv), and another embodiment includes step (ii). Only (iv).

The manufacturing method of this embodiment is
(I) heating citric acid or a citric acid derivative to obtain a condensate of citric acid or a citric acid derivative (hereinafter referred to as citric acid condensate);
(Ii) preparing a solution containing a citric acid condensate and a thermoplastic resin;
(Iii) heating the solution obtainable from step (ii) to obtain a solid,
(Iv) a step of heating and carbonizing the solid obtained from step (iii) in a non-oxidizing atmosphere;
It comprises.

  As described above, the mixture containing the citric acid condensate and the thermoplastic resin heated in the step (iv) is preferably a solid.

  First, step (i) will be described. Step (i) is a step of heating citric acid or a citric acid derivative to obtain a citric acid condensate.

  Examples of citric acid or citric acid derivatives include citric acid (including hydrates and anhydrides) and citric acid esters. These compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them. Of these compounds, citric acid is preferred. However, the citric acid derivative preferably does not contain a sulfur atom and a halogen atom, and more preferably does not contain a sulfur atom, a halogen atom, an alkali metal atom, and an alkaline earth metal atom.

  Although heating of the citric acid or a citric acid derivative in order to obtain a citric acid condensate is not specifically limited, For example, it can implement by irradiating a citric acid aqueous solution with a microwave. Another example of a heating method to obtain a citric acid condensate is Yongqiang Dong et al., “Blue luminescent graphene quantum dots and graphene oxide prepared by tuning the carbonization degree of citric acid”, Carbon, American Carbon Society, October 2012. , vol50, issue12, pp4738-4743.

  Citric acid condensate is known to have a graphene-like structure. This structure is formed by condensation of citric acid or a citric acid derivative. Even if citric acid was blended instead of the citric acid condensate or oxalic acid or tartaric acid was blended instead of the citric acid condensate, the yield of carbide from the thermoplastic resin was not significantly improved. From these experimental results, the present inventor believes that the graphene-like structure of the citric acid condensate suppresses the decomposition of the thermoplastic resin due to heating and improves the yield of the carbide. The graphene-like structure may be laminated to form a graphite structure. However, in the present invention, if a graphite structure exists, the structure difference from the surrounding amorphous part is large, and the structure is caused by electrical stimulation or the like. Since peeling occurs, the electrical durability as a carbon material may be lowered. Therefore, it is preferable not to include a graphite structure. The presence or absence of the graphite structure can be confirmed by a spectrum (X-ray diffraction spectrum) obtained using an X-ray diffraction method. Specifically, the presence or absence of a graphite structure can be confirmed by checking whether or not the X-ray diffraction spectrum has a peak in the range of diffraction angle (2θ) = 24 to 26 °.

  The citric acid condensate has a functional group derived from citric acid as well as a graphene-like structure. Depending on the type of the thermoplastic resin, it is considered that this functional group strengthens the bond between the citric acid condensate and the thermoplastic resin, and further enhances the effect of the yield of the carbide by blending the citric acid condensate.

  The citric acid condensate itself becomes a raw material for carbide. In addition, the addition of the citric acid condensate improves the yield of carbide from the thermoplastic resin while producing carbide substantially free of sulfur atoms and halogen atoms, and further, sulfur atoms, halogen atoms, alkali metals It makes it possible to produce carbides substantially free of atoms and alkaline earth metal atoms. In the present specification, “not containing substantially” means that the content is less than 1% by weight, preferably less than 0.1% by weight.

  Next, process (ii) is demonstrated. Step (ii) is a step of preparing a solution containing a citric acid condensate and a thermoplastic resin.

  The thermoplastic resin is not particularly limited in its type as long as it can form carbides, but in order to suppress the content of sulfur atoms, halogen atoms, alkali metal atoms and alkaline earth metal atoms in the carbides, these atoms are added. It is preferable to use a thermoplastic resin that does not substantially contain. The thermoplastic resin may be substantially free of sulfur atoms and halogen atoms. Specific examples of the thermoplastic resin include polyamide resins such as nylon-6 and nylon-66, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyether resins such as polyethylene oxide and polypropylene oxide, polyacetal resins, Polyacrylic resins, polystyrene, polystyrene resins such as styrene-acrylonitrile copolymers, styrene-butadiene-acrylonitrile copolymers, and polyvinyl alcohol resins.

  The thermoplastic resin preferably has a functional group containing a nitrogen atom and / or an oxygen atom. Specific examples of such a functional group include a carboxylic acid group, an ester group, an ether group, a hydroxyl group, an amino group, and an amide group. Specific examples of the resin include polyamide resin, polyester resin, polyether resin, polyacetal resin, polyacrylic resin, and polyvinyl alcohol resin. When such a thermoplastic resin is used, the decomposition of the thermoplastic resin is further suppressed by the interaction between the functional group of the thermoplastic resin and the functional group derived from citric acid of the citric acid condensate, for example, hydrogen bonding. It becomes possible.

  The thermoplastic resin is preferably a polyvinyl alcohol resin such as a polyvinyl alcohol resin or a polyvinyl alcohol resin analog from the viewpoint of the yield of carbide and reduction of impurities in the carbide. Examples of the polyvinyl alcohol resin analog include ethylene-modified polyvinyl alcohol resin.

  The shape of the thermoplastic resin is not particularly limited. For example, a block-shaped thermoplastic resin may be used, a pulverized thermoplastic resin having a specific particle size may be used, a thermoplastic resin granulated in a pellet shape or Raschig ring shape may be used, and spinning You may use the made fibrous thermoplastic resin.

  The solution containing the citric acid condensate and the thermoplastic resin can be obtained by mixing at least one of the citric acid condensate and the thermoplastic resin in a solvent. In order to uniformly mix the citric acid condensate and the thermoplastic resin, it is preferable to prepare a solution containing the citric acid condensate and the thermoplastic resin. A known method such as melt mixing in which a citric acid condensate is added to and mixed with a plastic resin may be used. Although the solvent which can be used when making it melt | dissolve in a solvent is not specifically limited, For example, alcohol, such as water, methanol, ethanol, cyclic ethers, such as tetrahydrofuran and 1, 4- dioxane, are mentioned.

  The mixing ratio of the citric acid condensate and the thermoplastic resin is, for example, 0.01 to 10000 parts by mass, preferably 0.1 to 10000 parts by mass, expressed by the mass part of the citric acid condensate with respect to 100 parts by mass of the thermoplastic resin. It is 2000 mass parts, More preferably, it is 0.5-1000 mass parts, More preferably, it is 1-500 mass parts. If the content of the citric acid condensate is too low, the yield of carbide will be low. When content of a citric acid condensate is too high, the influence of the physical property of a citric acid condensate with respect to the physical property of a carbide | carbonized_material will become large.

  Next, process (iii) is demonstrated. Step (iii) is a step of obtaining a solid by heating a solution containing a citric acid condensate and a thermoplastic resin. When step (iii) is carried out, it is considered that the citric acid condensate and the thermoplastic resin are likely to interact with each other.

  Step (iii) may be carried out under normal pressure, but is preferably carried out in a reduced pressure atmosphere. The reduced pressure atmosphere is, for example, 1 Pa to 40 kPa, preferably 10 Pa to 30 kPa.

  Further, step (iii) may be performed in an atmosphere different from the non-oxidizing atmosphere applied in step (iv). Step (iii) may be performed in an oxidizing atmosphere such as air.

  Step (iii) may be carried out at a temperature lower than the thermal decomposition temperature of the citric acid condensate and the thermoplastic resin, for example, 50 to 200 ° C. This temperature may be changed depending on the physical properties of the thermoplastic resin used. Although the time which implements process (iii) is not specifically limited, For example, it is 1 to 200 minutes.

  Next, step (iv) will be described. Step (iv) is a step of heating and carbonizing a solid containing the citric acid condensate and the thermoplastic resin in a non-oxidizing atmosphere.

  Heating of the solid containing the citric acid condensate and the thermoplastic resin is performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere may be an atmosphere in which the solid matter is not oxidized. Specifically, an atmosphere having an oxygen concentration of 0.1% by volume or less is preferable. The non-oxidizing atmosphere may be, for example, an atmosphere such as nitrogen, helium, or argon, and a nitrogen gas atmosphere is preferable.

  In the step (iv), the heating temperature is, for example, 300 to 800 ° C, preferably 400 to 600 ° C. If the heating temperature is too low, the carbonization reaction may not proceed sufficiently. If the heating temperature is too high, the condensation of the carbide may proceed too much. The heating temperature in step (iv) may be determined according to the thermal decomposition temperature and shrinkage temperature of the thermoplastic resin.

  The rate of temperature increase to the heating temperature is not particularly limited, and may be, for example, 0.1 to 50 ° C./min, particularly 1 to 20 ° C./min. If the rate of temperature increase is too slow, the energy utilization efficiency is poor and the manufacturing cost increases. If the rate of temperature increase is too fast, the decomposition reaction of the resin proceeds, and the yield of carbides may decrease. The cooling rate after carbonization is not particularly limited, and may be rapidly cooled using, for example, nitrogen gas or may be naturally cooled.

  Although the time which heats a solid substance with said heating temperature is not specifically limited, For example, it is good to set it as 1 to 500 minutes, especially 30 to 300 minutes. The equipment for carrying out the heating may be either a batch type or a continuous type in which the shape is selected with a tubular furnace, a box furnace or the like.

(X-ray diffraction spectrum)
Using MINIFLEX300 (manufactured by Rigaku Corporation), measurement was performed at a scanning range 2θ = 5 to 50 °. When no peak occurs in the range of 24 to 26 ° (2θ) of the obtained spectrum, it can be inferred that the graphite does not contain a graphite structure.

(Production Example 1)
In a 200 ml beaker, 21.0 g (0.1 mol) of solid citric acid monohydrate was added, and 50 ml of water was added to obtain a citric acid solution. The total amount of the obtained citric acid solution was put into an 800 W microwave irradiation apparatus and irradiated with microwaves for 20 minutes to obtain 7.0 g of a brown oily citric acid condensate.

(Production Example 2)
An oxalic acid condensate was obtained in the same manner as in Production Example 1 except that 20.0 g of oxalic acid was used in place of citric acid monohydrate.

(Production Example 3)
The tartaric acid condensate was obtained in the same manner as in Production Example 1 except that 20.0 g of tartaric acid was used instead of citric acid monohydrate.

Example 1
As a thermoplastic resin, 10 g of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., “PVA-217”) was dissolved in 200 g of ion-exchanged water. To this solution, 1.0 g of the citric acid condensate obtained in Production Example 1 was added to obtain a solution containing the citric acid condensate and a thermoplastic resin. Thereafter, this solution was heated to 60 ° C. under a reduced pressure of 1 Torr (0.133 kPa) to remove water. 14.3 g of a water-containing mixture was obtained. Thereafter, the water-containing mixture was heated in a vacuum dryer (80 ° C., 1 Torr) for 12 hours. Subsequently, 12.1 g of the obtained solid was put in a crucible and subjected to carbonization treatment by heating. The carbonization treatment was performed by raising the temperature at 10 ° C./min in a nitrogen atmosphere, keeping the temperature at 500 ° C. for 2 hours, and then naturally cooling. The recovered amount of carbide was 2.840 g.

(Example 2)
The same operation as in Example 1 was carried out except that the amount of the citric acid condensate was 2.0 g. The recovered amount of carbide was 3.447 g.

(Example 3)
The same operation as in Example 1 was carried out except that the amount of the citric acid condensate was changed to 5.0 g. The recovered amount of carbide was 4.642 g.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that only the polyvinyl alcohol was used without adding the citric acid condensate. The recovered amount of carbide was 2.328 g. The yield of carbide from polyvinyl alcohol was 23.28%.

(Comparative Example 2)
It implemented like Example 1 except having added 1.0g of citric acid and monohydrate instead of the citric acid condensate. The recovered amount of carbide was 2.339 g.

(Comparative Example 3)
It implemented like Example 1 except having added 1.0g of oxalic acid condensates obtained by manufacture example 2 instead of the citric acid condensate. The recovered amount of carbide was 2.318 g.

(Comparative Example 4)
It implemented like Example 1 except having added 1.0g of tartaric acid condensates obtained by manufacture example 3 instead of the citric acid condensate. The recovered amount of carbide was 2.122 g.

(Reference Example 1)
The same procedure as in Example 1 was carried out except that only 10 g of citric acid condensate was used without adding polyvinyl alcohol. The recovered amount of carbide was 1.422 g. The yield of carbide from the citric acid condensate was 14.22%.

The results obtained in Examples, Comparative Examples and Reference Examples are shown in Table 1. In Table 1, the yield [%] of carbide is the ratio of the recovered amount of carbide to the total amount of compounds such as added polyvinyl alcohol and citric acid condensate. Further, the rate of increase [times] of the carbide was determined based on the following formula.
Increase rate of carbide [times] = weight of obtained carbide [g] / assumed value [g]
The “assumed value” in the above formula is assumed to be obtained in each Example or Comparative Example calculated from the yield (Comparative Example 1, Reference Example 1) when each of the polyvinyl alcohol and citric acid condensate is carbonized alone. The amount of carbide to be calculated and calculated based on the following formula.
Assumed value [g] = 23.28 [%] / 100 × 10 [g] +14.22 [%] / 100 × A [g]
23.28 [%] is the yield of carbide using only polyvinyl alcohol (Comparative Example 1), and 14.22 [%] is the yield of carbide using only citric acid condensate (Reference Example 1). 10 [g] is the weight of the polyvinyl alcohol used in each Example or Comparative Example, and A [g] is the weight of the citric acid condensate.

Claims (9)

Step (i) of heating citric acid or a citric acid derivative to obtain a condensate;
Preparing a solution comprising the condensate and a thermoplastic resin (ii);
Heating the solution to obtain a solid containing the condensate and the thermoplastic resin (iii);
Wherein the solid non-oxidized by heating in an atmosphere to carbonize the solid step (iv), comprises a method for producing a carbide. A method for producing a carbide comprising the step (iv) of heating a mixture containing a condensate of citric acid or a citric acid derivative and a polyvinyl alcohol resin in a non-oxidizing atmosphere to carbonize the mixture. The manufacturing method of the carbide | carbonized_material of Claim 2 whose said mixture is a solid substance. The manufacturing method of the carbide | carbonized_material of Claim 3 which further comprises the process (iii) which heats the solution containing the said condensate and the said polyvinyl alcohol-type resin, and obtains the said solid substance. The manufacturing method of the carbide | carbonized_material of Claim 1 or 4 which implements the said process (iii) in a pressure-reduced atmosphere. The method for producing carbide according to claim 1, 4 or 5 , wherein the step (iii) is performed in an atmosphere different from the non-oxidizing atmosphere. A step (i) of heating citric acid or a citric acid derivative to obtain the condensate;
The method for producing carbide according to claim 4 , further comprising a step (ii) of preparing the solution containing the condensate and the polyvinyl alcohol-based resin . The method for producing carbide according to claim 1, wherein the thermoplastic resin has a functional group containing a nitrogen atom and / or an oxygen atom. Wherein the thermoplastic resin is a polyvinyl alcohol resin, method for producing a carbide of claim 1.

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