JP2014162718A - Crystalline carbon and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform heat treatment at a high temperature exceeding 2000 ° C. in the conventional synthetic carbon crystallization technology, or the crystallinity of the obtained carbon is insufficient, and additional elements remain. There are problems such as limited use, and because it is carbon derived from fossil resources, it cannot be covered by domestic resources and does not contribute to reducing greenhouse gas emissions. That is, the present invention is mainly intended to industrially advantageously obtain high-purity carbon having high crystallinity by heating a plant-derived material as a raw material at 2000 ° C. or lower. The above-mentioned problem is solved by adding calcium element and heating. It is recommended that the heating temperature be 1500 ° C. to 2000 ° C. or less.
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Description

  The present invention relates to the synthesis of high-purity crystalline carbon using plant-derived materials and a method for producing the same.

Carbon is classified into crystalline carbon and amorphous carbon, and it is known that the characteristics vary greatly depending on the presence or absence of crystallinity. For example, the oxidation start temperature in the atmosphere is greatly different in oxidation resistance from about 700 ° C. for crystalline carbon and about 400 ° C. for amorphous carbon. Furthermore, crystalline carbon has excellent characteristics in terms of thermal conductivity and electrical conductivity. Therefore, for example, crystalline carbon is used for applications that require excellent oxidation resistance, thermal conductivity, and electrical conductivity, such as refractories, heat-resistant crucibles, high-temperature furnace members and jigs, and electrode materials. ing.
Crystalline carbon includes natural raw materials such as scaly graphite and earthy graphite, and synthetic raw materials such as artificial graphite, but is available in quantities for applications that require a large amount of raw materials such as refractories. Natural raw materials are mainly used. However, natural raw materials such as scaly graphite have been declining in quality deposits in recent years, and the problem of resource depletion has been called out. Furthermore, natural carbon raw materials cannot be produced in Japan and all of them depend on imports from overseas. From these two sides, there is a strong demand for a technology that can stably supply a large amount of crystalline carbon at low cost in Japan.

  In addition, natural graphite having high crystallinity such as scaly graphite has a crystal interstitial distance d (002) value of about 0.335 nm, and it is known that this value increases as the crystallinity decreases. The higher the crystallinity, the better the properties such as oxidation resistance, thermal conductivity, and electrical conductivity. Therefore, when producing artificial graphite, the crystal interstitial distance is set to a value close to 0.335. It has been practiced to increase the crystallinity of carbon by heating at an extremely high temperature of ° C.

On the other hand, when carbon is exposed to an oxidizing atmosphere at a high temperature, it is oxidized and consumed to become CO ₂ gas, and finally released into the atmosphere as a greenhouse gas that causes global warming. In recent years, reductions in the amount of gas that causes global warming have been established, and carbon materials used in large quantities have problems with respect to the environment. In recent years, the concept of carbon neutral that does not change the amount of carbon in the environment has been advocated, and from the viewpoint of reducing CO ₂ emissions, carbon recycling technology using plant-derived biomass resources is active on a global scale, mainly in the energy field. Has been developed and put to practical use. If this biomass resource can be used as a raw material for synthesizing crystalline carbon, it will not be included in greenhouse gas emissions even when crystalline carbon is consumed during use, and it can be covered by domestic resources. It becomes a more ideal industrial raw material.

  In general, carbon obtained from plant-derived raw materials is classified as non-graphitizable carbon, and it is difficult to crystallize even if heat treatment is performed at a high temperature exceeding 2000 ° C. Therefore, in order to obtain crystalline carbon from plant-derived raw materials, enormous energy is required, which leads to a contradiction that a large amount of greenhouse gases are generated, which makes it difficult to put it to practical use in terms of the global environment and costs. Has been.

  Conventionally known methods for synthesizing crystalline carbon include a method of heating and crystallizing carbon obtained by processing petroleum and coal at an ultra-high temperature of about 3000 ° C., boron, silicon, iron, etc. There is a method of adding and heating.

For example, Patent Document 1 discloses a method of obtaining crystalline carbon by heat-treating carbon or a carbon precursor to which B ₄ C or boride and SiC are added simultaneously.

  Patent Document 2 discloses a method in which at least one element selected from boron, aluminum, silicon, calcium, titanium, and zirconium is added to carbon black, and crystalline carbon is obtained by induction heating. Yes.

  Furthermore, Patent Document 3 discloses a method of obtaining activated carbon by impregnating a wooden raw material with an aqueous solution of zinc chloride, calcium chloride, caustic soda, phosphoric acid or the like and firing at 500 to 700 ° C.

  On the other hand, in Non-Patent Document 1, after adding calcium chloride to lignite which is a kind of coal to make calcium exchange coal, iron or nickel is replaced with calcium by ion exchange to produce iron exchange nickel or nickel exchange coal, A method for obtaining crystalline carbon by heating it at a low temperature of 1000 ° C. or lower is shown.

  Non-Patent Document 2 discloses a method of obtaining crystalline carbon by adding nickel or iron to wood and heating it at a low temperature of 1000 ° C. or lower.

  Japanese Patent Laid-Open No. 10-153212   JP 2002-265 211 A   JP 11-349320 A

  Kenji Murakami, Kiyoshi Fuda, Mikio Sakurai (Akita University) “Effects of ion-exchange metals on carbonization of lignite” Journal of MMIJ. vol. 125. p38-42 (2009)   Hokkaido Development Bureau Development Supervision Department, Development Research Section, “Survey of energy and material utilization of wood by high-performance carbon conversion in 2006” Business Report, p92-96 (March 2007)

  These conventional methods are methods in which carbon obtained by processing petroleum or coal is crystallized by heating at an extremely high temperature of about 3000 ° C., and enormous energy is consumed for the heat treatment. For this reason, there is a problem that the cost becomes very high and the quantitative supply is difficult. There are also some problems with the method of heating by adding boron, silicon, iron or the like to carbon.

For example, Patent Document 1 shows that the temperature required for crystallization of carbon is 2600 ° C. or higher, and there is a problem that the energy cost increases because high temperature heating of 2000 ° C. or higher is required. Further, although not explicitly stated in the literature, it is presumed that the added boron and silicon are present in the heated carbon in the form of B ₄ C, SiC, or solid solution. When these are oxidized and used under conditions that change to boron oxide or silica, the corrosion resistance against basic slag and the like is reduced.

  In Patent Document 2, additives such as boron, aluminum, silicon, calcium, and titanium are used, but all of the additives are used as a heat energy source for causing a self-heating reaction, and the present invention. It is completely different from the target.

Furthermore, Patent Document 2 does not include content that suggests the effect of promoting the crystallization of carbon by the addition of calcium element intended by the present invention. Moreover, the value of the interstitial distance d (002) of the obtained carbon crystal is in the range of 0.340 to 0.344 nm, which is larger than the value of natural scaly graphite of 0.335 nm, and crystallization is insufficient. Since added boron, titanium, and the like are also present in the heated carbon as B ₄ C and TiC, when they are used under conditions where they are oxidized to change to boron oxide or titania, the base There is a problem of causing a decrease in corrosion resistance against slag and the like.

  Non-Patent Document 1 discloses a method of supporting calcium on brown coal. This is used as an intermediate means for improving the ion exchange efficiency when iron and nickel are subsequently supported by ion exchange with iron and nickel, and is completely different from the object of the present invention. ing. In addition, carbon, obtained by heating, contains additional elements such as iron, nickel, calcium, etc., so when they are used under conditions that oxidize and change to iron oxide, nickel oxide, calcia Has a problem of reducing the corrosion resistance against acid slag and the like.

  In both Patent Documents 1 and 2 and Non-Patent Document 1, fossil resources such as oil and coal are used as starting materials for obtaining carbon, which is covered by domestic resources, together with the problem of not contributing to the reduction of greenhouse gas emissions. There is no problem.

  Patent Document 3 discloses a method of impregnating a wood raw material with an aqueous calcium chloride solution. Calcium chloride in Patent Document 3 is used as an activation chemical having a carbon activation function, and is completely different from the object of the present invention. Moreover, the content which suggests about the crystallization promotion effect of carbon by addition of the calcium element which this invention intends is not contained. Furthermore, activated carbon obtained by heating is activated carbon that is not crystallized and has many fine open pores. When used under high-temperature oxidizing atmosphere conditions, the activated carbon is resistant to oxidation. There is a problem of bringing about a decrease.

  In Non-Patent Document 2, the value of the interstitial distance d (002) of the obtained carbon crystal is in the range of 0.338 to 0.341 nm, which is larger than the value of natural scaly graphite 0.335 nm, and crystallization is not possible. It is enough. In addition, since iron and nickel remain in the carbon obtained by heating, when used under conditions that oxidize and change to iron oxide or nickel oxide, corrosion resistance to acidic slag, etc. There is a problem of bringing about a decrease. Non-Patent Document 2 shows that acid cleaning is performed as a method for removing the remaining additive elements. However, acid cleaning is performed after heat treatment, and steps such as neutralization treatment, final washing, and drying treatment are performed. Adding it causes an increase in cost, and there is also a problem that it is difficult to sufficiently remove a metal element finely contained in carbon.

  In the conventional crystallization technique, heat treatment at a high temperature exceeding 2000 ° C. is necessary, or the crystallinity of the obtained carbon is insufficient, and additional elements remain, so that the use is limited. Furthermore, since it is carbon derived from fossil resources, there is a problem that domestic resources cannot cover the greenhouse gas emission control.

  The present invention is intended to solve these problems, and in particular, an intensive study on additive elements that can promote the crystallization and high purity of carbon by heating at 2000 ° C. or lower using plant-derived materials as raw materials. As a result, the present invention was completed. That is, an object of the present invention is to provide high-purity carbon having high crystallinity by heating at 2000 ° C. or less using a plant-derived material as a raw material.

  The crystalline carbon according to the present invention is characterized by adding calcium element to a plant-derived material and heating it as a technical configuration for achieving the above object (claim 1). Moreover, in crystalline carbon heated by adding calcium element to a plant-derived material, the heating temperature is 1500 ° C. to 2000 ° C. (Claim 2). Furthermore, the method for producing crystalline carbon according to the present invention is characterized by adding calcium element to a plant-derived material and heating at 1500 ° C. to 2000 ° C. or less as a technical configuration that also achieves the object. Item 3).

  The present invention is characterized in that a crystalline carbon having high crystallinity and purity is obtained by adding calcium element to a plant-derived material and heating it. This makes it possible to obtain high-performance crystalline carbon excellent in various properties from domestic resources at low cost and provide high-quality synthetic crystalline carbon to various industries without depending on imported resources. can do.

  Hereinafter, the effects of the present invention will be described in detail, and further embodiments of the present invention will be described.

  As a result of repeated studies on a method for generating high purity carbon with excellent crystallinity using domestic resources as a starting material, the present invention has found that it is very effective to add calcium element to plant-derived materials and heat them. The present invention has been completed.

  The present invention is a carbon derived from fossil resources, heat treatment at a high temperature exceeding 2000 ° C. in the conventional crystallization technique, insufficient crystallinity of the obtained carbon, limited use due to residual additive elements, and fossil resources. Therefore, it provides an effective means to solve the problem that domestic resources cannot cover the greenhouse gas emission control, and it is different from the conventional carbon crystallization technology. It provides new synthesis technology in the field of materials using crystalline carbon.

  The elemental calcium used in the present invention is a crystal of carbon when heated at a temperature higher than that after the plant-derived material is carbonized by heating up to about 1000 ° C. by heating in a state coexisting with the plant-derived material. Demonstrates the effect of significantly promoting crystallization. This crystallization action by the calcium element is remarkably expressed when a plant-derived material is used as a raw material. In general, carbon obtained from wood and the like is classified as non-graphitizable carbon, but crystallizes at a lower temperature than carbon black, etc., so that calcium acts on carbon having a structure that is easily crystallized from the beginning. It is considered that a remarkable crystallization action was developed. To elucidate the reaction mechanism, further advanced research is required. However, when a compound containing calcium element melts, reacts, and evaporates when heated, it facilitates the transfer and rearrangement of carbon atoms. There is a possibility that a catalytic action that promotes crystallization of carbon generated from the derived substance is generated.

  In general, calcium oxide is known to be thermodynamically stable and difficult to evaporate even at high temperatures, and it is considered in the conventional common sense that calcium element is included when trying to obtain high purity carbon. I couldn't. In the present invention, by heating in a state where calcium element and carbon coexist, calcium is evaporated and disappears from the carbon, so that the effect of increasing the purity of the carbon can be obtained. The mechanism by which calcium element evaporates at high temperatures is not clear, but coexistence with carbon keeps the oxygen partial pressure low during heating, creating conditions that facilitate the formation of carbides such as calcium carbide, and vapor pressure is reduced. It is possible that it has risen.

  The calcium element used in the present invention can be added in any form such as chloride, nitrate, sulfate, carbonate, hydroxide, oxide, fluoride. Among these, those that can be used in a solution state such as an aqueous solution such as calcium chloride and calcium nitrate are more preferable in terms of enhancing dispersibility. In these compounds, elements other than calcium may coexist, and for example, elements other than calcium may be contained as impurities.

  The plant-derived material used in the present invention means various plant-derived raw materials classified as biomass, and representative examples that can be obtained quantitatively as domestic resources include wooden materials, rice husks, tea husks, coffee husks, coconut husks, Examples include papermaking replicas. As the wood material, various kinds of trees such as cedar, straw, oak, cherry blossom, pine and bamboo can be used, and any material such as branches, trunks, and bark can be used. In particular, by using bark that has not been reused, natural resources can be used more effectively. In addition, although fossil resources such as oil and coal are derived from ancient plants, these are not regarded as so-called biomass. Therefore, various raw materials synthesized by processing oil and coal are The plant-derived material used in the present invention is not intended.

  The pretreatment of the plant-derived material used in the present invention is not particularly limited, but is used after removing free water or the like by a drying treatment in the sense of increasing the heating efficiency by reducing the gas generated during the heat treatment. Is desirable.

  Moreover, the plant-derived material used in the present invention can be used as carbonized by preheating or partially advanced pyrolysis reaction. A plant-derived material is preheated, and a pyrolysis reaction is advanced to remove volatile components and the like, and calcium element can be added and heated. The preheating condition is not particularly limited, but may be a temperature of 800 ° C. or more, which is generally said to cause the carbonization reaction to be almost completed by the progress of the pyrolysis reaction. You may use in the state which heated at about 300-700 degreeC, and was thermally carbonized in the state in which the thermal decomposition reaction is progressing.

  In the method of adding calcium element to the plant-derived material of the present invention, a simple element of calcium element or a compound or the like may be used as a solid such as powder or granule, or may be used as a solution state such as an aqueous solution. From the viewpoint of increasing the dispersibility of the calcium element in the plant-derived material, it is effective to use it in a solution state such as an aqueous solution. When calcium element is added in a solution state, the concentration is in the range of 0.2 to 2 mol / L from the viewpoint of increasing the purity and yield of the obtained crystallized carbon while obtaining sufficient carbon crystallization action. More effective. If the concentration of the solution is less than 0.2 mol / L, crystallization of the obtained carbon is relatively difficult to proceed, and if it exceeds 2 mol / L, the purity and yield of the crystallized carbon tend to be low, which is more preferable. A concentration range of 0.2 to 2 mol / L is recommended.

  In the present invention, heating a plant-derived material containing calcium element is an essential condition. The heating needs to be performed under temperature conditions that can achieve both crystallization and high purity of carbon, and is preferably in the range of 1500 ° C to 2000 ° C. If the temperature is less than 1500 ° C., the crystallization and purification of carbon intended by the present invention will not proceed sufficiently. When it exceeds 2000 ° C., the energy cost increases, which is not preferable. It is more preferable to set the temperature to 1600 ° C. to 1800 ° C. in order to further promote the crystallization and high purity of carbon and to keep the energy cost low. The holding time at the heating temperature is more effective for 8 hours to 20 hours. If it is less than 8 hours, the added calcium element remains and the purity tends to be low, and if it exceeds 20 hours, the energy cost increases. Therefore, more preferably, a holding time of 8 hours to 20 hours is recommended. The

  In the present invention, it is desirable that the atmospheric condition during heating is an inert atmosphere. For example, by heating under a low oxygen partial pressure such as an argon gas atmosphere, a nitrogen gas atmosphere, or a vacuum atmosphere, it is possible to prevent loss of oxidation of carbon and promote high purity.

  The crystalline carbon intended by the present invention is required to contain at least a part of the crystalline phase of carbon. There are two known crystal structures of carbon, a diamond structure and a graphite structure, but a graphite structure is common as a material that can be produced under conditions near atmospheric pressure, and the crystalline carbon of the present invention is also graphite. Intended for crystals. Whether or not a carbon crystal is contained can be easily known by an X-ray diffraction method. For example, the obtained carbon is pulverized into a powder form, and a diffraction pattern of the graphite crystal 002 plane appears near a diffraction angle of 26 ° by measuring a diffraction pattern by a powder X-ray diffraction method using CuKα rays. It can be easily determined that a carbon crystal phase is contained therein. That is, it is essential for the crystalline carbon of the present invention that a diffraction peak corresponding to the 002 plane of a graphite crystal appears in a diffraction pattern measured by an X-ray diffraction method.

  In the crystalline carbon of the present invention, the crystal phase contained in at least a part of the crystalline carbon is more preferably close to an ideal graphite crystal. The closer the crystal structure is to an ideal graphite crystal, that is, a natural scaly graphite crystal, is expected to exhibit superior performance in oxidation resistance, corrosion resistance, etc. when actually used. The crystal structure of the carbon crystal phase can be known from the diffraction peak measured by the X-ray diffraction method. For example, the closer the interstitial distance d (002) on the 002 plane obtained from the diffraction peak position of the graphite crystal described above to the value of 0.335 nm in natural scaly graphite, the less the disordered ideal crystal structure. Recognize.

  Next, the present invention will be described in more detail with reference to examples of the present invention. However, the present invention is not limited to the following examples.

[Examples 1 to 3, Comparative Examples 1 to 6]
Cedar bark and phenol resin were used as starting materials for obtaining carbon, and various compounds CaCl ₂ , FeCl ₃ , BaCl ₂ , AlCl ₂ , MgCl ₂ , YCl ₃ , and Ca (NO ₃ ) _{2 were} added thereto. The compound to be added was prepared in advance as an aqueous solution and adjusted so as to have a concentration of 1 mol / L. The bark was immersed in various aqueous solutions so as to penetrate the phenolic resin, and the phenol resin was mixed and the water was evaporated by a drying treatment. Also, it was also prepared by mixing CaCl ₂ · 2H ₂ O in powder bark. The bark and phenol resin to which these various compounds were added were embedded in carbon powder and heated at 1000 ° C. for carbonization. The obtained carbide was taken out from the carbon powder, and then heated at 1500 ° C. and 1600 ° C. in an argon gas atmosphere.

  The obtained carbon was pulverized into powder, and the diffraction pattern due to the crystal phase was measured using an X-ray diffractometer. The measurement was performed under the conditions of 40 kV and 30 mA using CuKα rays. Whether or not a carbon crystal phase exists was evaluated by paying attention to the strongest peak of graphite crystals appearing around 26 °. For those in which a diffraction peak of carbon crystal was observed, the peak intensity was measured at a scanning speed of 0.2 ° / min.

  The test results are shown in Table 1. As is clear from Table 1, in Examples 1 and 2 of the present invention, the peak intensity of the graphite crystal 002 plane in the X-ray diffraction pattern is significantly larger than those in Comparative Examples 1 to 6, and the crystallization of carbon Is clearly progressing. Further, in Example 3 of the present invention, although the holding time at 1500 ° C. is 0 hour, the peak intensity of the graphite crystal 002 plane is significantly larger than those of Comparative Example 1 and Comparative Examples 3 to 6, and It can be seen that crystallization is clearly progressing.

[Examples 4 to 9, Comparative Example 7]
Cedar and birch bark were used as starting materials, and CaCl ₂ was added thereto. The CaCl ₂ to be added was previously made into an aqueous solution and adjusted so that the concentration was 0.7 mol / L. After immersing the bark in the prepared aqueous solution to infiltrate and evaporating water by a drying treatment, the water was embedded in carbon powder and heated at 1000 ° C. to be carbonized. The obtained carbide was taken out from the carbon powder, and then heated in an argon gas atmosphere in a temperature range of 1300 to 2000 ° C.

  The obtained carbon was pulverized into powder, and the diffraction pattern due to the crystal phase was measured using an X-ray diffractometer. Measurement was performed under the conditions of 40 kV and 30 mA using CuKα rays. Whether or not it exists in the crystal phase of carbon is evaluated by paying attention to the strongest peak of the graphite crystal appearing at around 26 °. Measurement was performed at 2 ° / min, and the interstitial distance d (002) of the graphite crystal 002 plane was calculated from the position of the diffraction peak. In addition, when a crystalline phase other than carbon was detected, the peak intensity was also measured.

  The test results are shown in Table 2. As is clear from Table 2, in Examples 4 to 9 of the present invention, the peak intensity of the graphite crystal 002 plane in the X-ray diffraction pattern is remarkably larger than that in Comparative Example 7, and the crystallization of the coal line is evident. It can be seen that it is progressing. In addition, the crystalline carbon obtained in Examples 4 to 9 of the present invention has an interstitial distance d (002) of 0.336 to 0.337 nm, which is close to the value of natural scaly graphite 0.335 nm, and is not disturbed. There are few crystal structures. Further, from the comparison of Examples 4 to 6 of the present invention, the peak of the calcium compound is detected when the retention time at the heating temperature is 0 hour and 6 hours, but it is not detected when the retention time is 12 hours. By making it longer, crystalline carbon with higher purity can be obtained.

[Examples 10 to 17]
Cedar and birch bark were used as starting materials, and CaCl ₂ was added thereto. The CaCl ₂ to be added was prepared in advance as an aqueous solution and adjusted so as to have a concentration of 0.1 to 5.4 mol / L. After immersing the bark in the prepared aqueous solution to infiltrate and evaporating water by a drying treatment, the water was embedded in carbon powder and heated at 1000 ° C. to be carbonized. The obtained carbide was taken out from the carbon powder, and then heated at 1500 ° C. and 1600 ° C. in an argon gas atmosphere.

  The obtained carbon was pulverized into powder, and the diffraction pattern due to the crystal phase was measured using an X-ray diffractometer. Measurement was performed under the conditions of 40 kV and 30 mA using CuKα rays. Whether or not a carbon crystal phase exists is evaluated by paying attention to the strongest peak of the graphite crystal appearing at around 26 °. Measurement was performed at 2 ° / min, and the interstitial distance d (002) of the graphite crystal 002 plane was calculated from the position of the diffraction peak.

  The test results are shown in Table 3. As apparent from Table 3, all of Examples 10 to 17 of the present invention have large peak intensity on the graphite crystal 002 plane, and the interstitial distance d (002) is 0.336 to 0.337 nm, which is natural scaly graphite. Since this value is close to 0.335 nm, it can be seen that the crystallization of carbon proceeds and the crystal structure is less disturbed. Further, when the concentration of the aqueous solution of the calcium compound is 0.3 mol / L, the peak intensity of the graphite crystal 002 plane is larger than that of 0.1 mol / L. Carbon is obtained.

  From the above, it is clear that the crystalline carbon of the present invention and the method for producing the same can provide high-purity carbon having high crystallinity by heating at 2000 ° C. or less using a plant-derived material as a raw material.

Claims (3)

  Crystalline carbon characterized by adding elemental calcium to a plant-derived material and heating it.   The crystalline carbon according to claim 1, wherein the heating temperature is 1500 ° C. to 2000 ° C.   A method for producing crystalline carbon, comprising adding calcium element to a plant-derived material and heating at 1500 ° C to 2000 ° C.