Method for producing carbon material

Abstract

The purpose of the present invention is to provide a production method capable of contributing to a reduction in CO2 by using a carbon material produced from a plant-based raw material and capable of reducing production costs, etc.　The present invention relates to a method for producing a carbon material, the method being characterized by comprising: a washing step in which a plant-based raw material is immersed in an aqueous solution, stirred, and washed; a dewatering step in which the plant-based raw material is stored in a container after the washing step, rotated by a rotary dewatering device, and the plant-based raw material is dewatered; and a firing step in which the plant-based raw material in a damp state is fired without drying after the dewatering step.

Description

Carbon material manufacturing method

[0001] The present invention relates to a method for producing a carbon material such as graphene from a plant-derived raw material.

[0002] Plant-derived raw materials have traditionally been used for battery materials, conductive materials, heating elements, tires, building materials, etc. from the perspective of carbon neutrality. In particular, carbon materials with a large specific surface area have been used as materials for batteries and capacitors. Carbon materials with excellent electrical conductivity have also been widely used as heating materials and shielding materials.

[0003] As such, various inventions have been proposed as methods for producing carbon materials from plant-based raw materials. For example, Patent Document 1 describes a method for producing a carbon material, in which a carbonaceous raw material is activated with an alkali metal compound to obtain activated carbon or activated carbon fiber with a high specific surface area, by surrounding the reaction system (a composition containing the carbonaceous raw material and the alkali metal compound) with a carbon-based powder layer and, if necessary, further including an inorganic compound layer in the carbon-based powder layer for activation. Also, a method for producing a carbon material, in which the temperature rise rate during activation is set to 20°C / hr or less, thereby increasing the yield of the carbon material per container. An electric double layer capacitor uses activated carbon or activated carbon fiber obtained by the production method as an electrode material.

[0004] For example, Patent Document 2 discloses an invention that includes a pretreatment step (S1) of drying a plant-derived raw material, drying and pulverizing it to obtain a carbon source, a carbonization step (S2) of carbonizing the carbon source to obtain a carbonized product, and a purification step (S3) of removing impurities including silica from the carbonized product obtained in the carbonization step, wherein the carbonization step includes a heating step of supplying an inert gas into a chamber and heating the carbon source in the chamber in a plasma atmosphere.

[0005] JP 2002-362915 A JP 2020-55727 A

[0006] As described in the patent documents, methods for producing carbon materials from plant-based raw materials involve activation using various chemicals. Porous carbon materials are produced using chemicals such as strong alkalis, which causes severe metal corrosion during the carbonization and other firing processes, shortening the lifespan of the equipment. Furthermore, there is a need for a production method that minimizes the number of production steps and reduces production costs. Furthermore, when used as a battery material, it is necessary to remove silicon to increase the purity of the carbon material in order to improve the specific surface area.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a production method that can contribute to CO2 reduction by using a carbon material produced from plant raw materials and can reduce production costs, etc.

[0008] A method for producing a heat-generating paint, characterized in that a carbon material produced from plant-based raw materials is mixed and dispersed in a synthetic resin emulsion.

[0009] Due to the above features, the present invention can contribute to CO2 reduction by using carbon materials produced from plant-based raw materials, and can provide a heat-generating paint that can maintain its strength even in various temperature ranges.

[0010] 1 is a Raman spectrum of graphene according to an embodiment; 2 is a Raman spectrum of a carbide according to an embodiment; 3 is a schematic diagram showing the configuration of a heating element coated with a heat-generating paint according to an embodiment; 4 is a schematic diagram showing the temperature characteristics of a heating element according to an embodiment; 5 is a schematic diagram showing the temperature characteristics of a heating element according to an embodiment; 6 is a schematic diagram showing the configuration of a plasma device according to an embodiment; 7 is a diagram showing a process flow showing a manufacturing process for producing a carbon material according to an embodiment; 8 is a diagram showing a process flow showing a manufacturing process for producing a carbon material according to an embodiment; 9 is a conceptual diagram of another example of a neutralization treatment according to an embodiment; 10 is a conceptual diagram of another example of an apparatus used in the neutralization treatment according to an embodiment; 11 is a diagram showing a process flow showing a manufacturing process for producing a carbon material according to an embodiment; 12 is a schematic diagram showing the configuration of a heating element according to an embodiment; 13 is a schematic diagram showing the configuration of a heating element according to an embodiment; 14 is a schematic diagram showing the configuration of a heating element according to an embodiment; 15 is a schematic diagram showing the configuration of a heating element according to an embodiment;

[0011] The heat-generating paint of the present invention will be described in detail with reference to the drawings. Note that the embodiments and drawings described below are intended to exemplify some of the embodiments of the present invention, and are not intended to limit the present invention to these configurations, and can be modified as appropriate within the scope of the present invention.

[0012] <Biomass Material> The plant raw material 9 for producing graphene will be described. The present invention produces graphene, which is a final product, using food residues or discarded plant raw material 9. Plants, wood, etc. are used as the plant raw material 9, but in particular, if discarded plant raw material 9 such as residues after harvesting plants is used as the raw material for producing graphene, it is possible to obtain the raw material at low cost.

[0013] Table 1 is a table of ingredients for plant-based raw material 9. In Table 1, the proportions of the ingredients constituting the raw material shown on the far left are shown as percentages on the right. For example, rice straw contains 37.4% carbon (C), 0.53% nitrogen (N), 0.06% phosphorus (P), 0.14% phosphoric acid (PO), 1.75% potassium (K), 2.11% potash (KO), 0.05% calcium (Ca), 0.19% magnesium (Mg), and 0.11% sodium (Na).

[0014] Here, plant-derived silicon-containing porous plant material 9 undergoes no substantial change even when carbonized at low temperatures (300°C or higher and 1000°C or lower), and the arrangement of pores can be maintained by removing the silicon. Many plant materials 9 have a structure in which cells are regularly arranged along their axes, with thickened cell walls due to the deposition of silicic acid. Furthermore, there are compressed, narrow cell rows between the silicified cell rows, and by removing silicon and other components after carbonization, a carbon material with a high specific surface area can be obtained. As mentioned above, a plant material 9 containing a high amount of silicic acid, between 13% and 35%, is suitable. Too much silicic acid results in less graphene being obtained, so a plant material 9 with a silicic acid content of around 20% is preferable.

[0015] Examples of carbon-rich plant materials 9 are shown in Table 1, and include, in addition to rice straw, wheat straw, barley straw, wheat husks, barley husks, cocoa husks, rice bran, rice husks, buckwheat straw, soybean vines, sweet potato vines, turnip leaves, carrot leaves, corn stalks, sugarcane tops, sake lees, coconut shells, coconut meal, peanut shells, mandarin peels, coffee husks, coffee grounds, red cedar sawdust, larch bark, fallen ginkgo leaves, tomato branches and trunks, and grape branches and trunks. Plants themselves may also be used instead of residues.

[0016] For example, bamboo is made up of cellulose, hemicellulose, and lignin as cellulose components, and minerals such as iron, magnesium, calcium, manganese, copper, and nickel. When bamboo leaves are burned, silanol groups (Si-OH) are extracted, and are converted into SiO4 during the burning process.

[0017]

[0018] Tables 2 and 3 are tables showing the composition of the plant raw material 9 that is most suitable for the method of producing a carbon material in the present invention, among the plant raw materials 9 in Table 1 described above. Table 2 shows the proportions of the components that make up the raw material in percentage. For example, moisture is 8% to 10%, ash is 10% to 18%, lipids are 0.1% to 0.5%, lignin is 18% to 25%, hemicellulose is 16% to 20%, cellulose is 30% to 35%, and others are 5% to 10%. Thus, the main components that make up silica ash 19 are lignin, hemicellulose, and cellulose.

[0019] Table 3 shows the chemical composition of the inorganic matter in the plant-based raw material 9 shown in Table 2. The plant-based raw material 9 shown in Table 2 contains 80 wt% organic matter such as cellulose and 20 wt% inorganic matter. The chemical composition of the inorganic matter in Table 3 is 92.14 wt% SiO2, 0.04 wt% Al2O3, 0.48 wt% CaO, 0.03 wt% Fe2O3, 3.2 wt% KO, 0.16 wt% MgO, 0.18 wt% MnO, and 0.09 wt% Na2O. The plant-based raw material 9 shown in Table 2 contains a large amount of silicon oxide (SiO2) in the inorganic matter.

[0020] (Example) <Process Flow 1> Referring to FIGS. 6 and 7 , the manufacturing steps of a method for producing graphene 113 and carbide 19 will be described. FIG. 7 is a diagram showing a process flow illustrating the manufacturing steps of an embodiment. First, in the pretreatment step S1, after drying the plant-based raw material 9 as described above, the plant-based raw material 9 is pulverized. The pulverized plant-based raw material 9 is mixed with a granulating agent such as PVA in a ratio of 10:1 and water to form the plant-based raw material 9 into particles of appropriate size, which are then kneaded together. The mixture is then heated to approximately 100°C on a drying device such as a hot plate to evaporate the water, thereby producing the plant-based raw material 9. Examples of the pulverization method include a mill, a mixer, a grinder, and the like. In particular, the granulating agent can prevent bumping of the plant-based raw material 9 due to steam during induction heating.

[0021] Next, the carbonization step S2 will be described. In the pretreatment step S1, approximately 0.8 g of plant-derived raw material 9 is placed in a crucible 5 and covered with a metal mesh or the like. The crucible 5 is placed in a predetermined heating position in the plasma device 10 described above. The pressure inside the chamber 1 is reduced to 80 Pa using a vacuum pump 30, and an inert gas 6 is injected into the chamber 1 at a flow rate of 8 to 10 ml / min, so that the pressure inside the chamber 1 is maintained at 1300 to 1500 Pa. Note that in the carbonization step S2, similar graphene can be produced using Examples 1 and 3.

[0022] The highest yield of 36% was measured at 500°C to 800°C, and relatively high yields were obtained at temperatures above 300°C and below 1000°C. In this measurement, rice straw, bran, coconut shells, rice husks, peanut shells, etc. were used, and similar results were obtained. In the carbonization step S2, the plant-derived raw material 9 is carbonized in about 10 to 30 minutes by heating at a temperature range of 300°C to 1000°C using thermal plasma generated by arc discharge while an inert gas 6 is being introduced.

[0023] Next, the activation step S3 will be described. The carbide 19 obtained above was mixed with potassium hydroxide in a weight ratio of 1 part to 5 parts, and the mixture was placed in a small crucible and covered with a lid. The small crucible was then placed inside a large crucible, and activated carbon was embedded around it. The activated carbon was embedded to prevent oxygen from entering the small crucible. The heating furnace was heated to a temperature of nearly 950°C, and the mixture was fired for approximately 2 to 3 hours.

[0024] Here, potassium hydroxide is used to promote the removal of silicon and therefore to improve the yield of the final product, graphene 113. Examples of bases include alkali metal hydroxides such as sodium hydroxide and lithium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, alkali metal oxides such as sodium oxide and potassium oxide, alkaline earth metal oxides such as magnesium oxide and calcium oxide, alkali metal sulfides such as sodium sulfide and potassium sulfide, and alkaline earth metal sulfides such as magnesium sulfide and calcium sulfide. Alternatively, it is also possible to remove lignin that has not been completely carbonized with one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, PTSA, and aluminum chloride.

[0025] Of the carbide 19 reacted with potassium hydroxide, silicic acid reacts with potassium hydroxide to form potassium silicate, and the remaining water-soluble potassium hydroxide (KOH) and potassium silicate are dissolved in water, and the resulting mixture is placed on filter paper and passed through a vacuum or reduced-pressure filter to remove silicon oxide (silicon). Then, in the drying activation step S3, it was possible to produce graphene 113, which is the final product, with a weight that is about 1 / 8 to 1 / 10 of that when the initial plant-derived raw material 9 was granulated.

[0026] The plasma device 10 of this embodiment will be described with reference to Fig. 6. Fig. 6 is a schematic diagram showing the configuration of the plasma device 10 of this embodiment. The plasma device 10 is mainly composed of an inert gas 6, a control device 20, a chamber 1, and a vacuum pump 30.

[0027] The inert gas 6 stored in the gas cylinder is mainly argon, but other examples include helium, neon, nitrogen, etc. The inert gas 6 can be filled into the chamber 1 via an inlet pipe 7 and a gas amount control device 21. The gas amount control device 21 can adjust the flow rate of the inert gas 6.

[0028] Chamber 1 is connected to control valve 22, and the pressure inside chamber 1 can be reduced to a vacuum state by vacuum pump 30. It is connected to chamber 1, and an inert gas 6 is introduced into chamber 1. A leak valve 23 that releases the vacuum state inside chamber 1 to atmospheric pressure is provided between control valve 22 and chamber 1. In addition, a control valve 14 and a leak valve 15 that releases the vacuum state inside chamber 1 to atmospheric pressure are also provided between outlet pipe 8 that introduces air inside chamber 1 and vacuum pump 30.

[0029] The temperature control device 24 also controls the high-frequency power supply 4, managing the temperature maintenance and maintenance time within the chamber 1. The plasma device 10 of this embodiment uses an inert gas (argon gas) 6 as a working gas under a low pressure close to a vacuum, and a high current is passed between the electrodes (cathode 2 and anode 3) to generate thermal plasma by arc discharge. A carbon crucible 5 is placed between the cathode 2 and anode 3, and the crucible 5 contains a plant-derived raw material 9 (described below). The plant-derived raw material 9 is heated to a temperature range of 300°C to 1000°C by the thermal plasma generated by the arc discharge, and is carbonized in approximately 10 to 30 minutes. In addition to the plasma device described above, other methods of generating thermal plasma include barrier discharge, corona discharge, pulse discharge, and DC discharge.

[0030] In the above manufacturing method, a gas phase reaction occurs, and by mixing a small amount of reactive gas such as inert gas 6, functional groups such as -OH (hydroxyl group), -CHO, -C=O (carbonyl group), and -COOH (carboxyl group) are generated, imparting hydrophilicity. The manufacturing method is not limited to the above. The heat source may be induction heating, gas, or an electric furnace, in addition to the plasma device.

[0031] In the case of induction heating, even if the plant-derived raw material 9 contains an insulating material such as silicon dioxide (SiO2), the magnetic flux passes through, making the plant-derived raw material 9 conductive, and the plant-derived raw material 9 itself is heated, and the heating is accelerated, allowing the plant-derived raw material 9 to be carbonized in a short period of time.

[0032] Furthermore, since the insulating material such as silicon dioxide (SiO2) itself allows the alternating magnetic flux to pass through, the silicon dioxide (SiO2) itself is only heated from the storage box 205 and is not at a temperature that would melt it, so it remains as it is, and much of the insulating material such as silicon dioxide (SiO2) remains.

[0033] <Process Flow 2> Fig. 8 shows a main flow of a manufacturing method for manufacturing the carbon material 100. In this example, a method for manufacturing the carbon material 100 to be converted into graphene will be described based on the flow from S11 to S16.

[0034] First, the plant-derived raw material 9 is pulverized in a pulverizer, but since the plant-derived raw material 9 is held in a dehydration container 15 with slits, holes, or a mesh, as described below, for dehydration, a carbon source pulverization process (S11) is performed to pulverize the plant-derived raw material to a degree that does not result in an excessively fine powder. The carbon source pulverization process (S11) may be performed to a degree that allows the alkaline aqueous solution to easily penetrate the plant-derived raw material in the next process. Note that S11 does not necessarily have to be performed first, and may be performed last.

[0035] Next, the crushed plant raw material 9 is subjected to an aqueous solution infiltration treatment (S12) in which the plant raw material 9 is reacted with an alkaline aqueous solution 20 at a temperature of 60° C. or higher for 1 to 10 hours. The most efficient production is achieved by providing a reaction step for about 4 hours.

[0036] In addition, this step (S12) may be a method of immersing the plant-derived raw material 9 in the aqueous solution 20 at room temperature for about one week. In this case, it is possible to adjust the pH of the aqueous solution 20 and use a weakly alkaline aqueous solution 20 with a pH of about 9.

[0037] The concentration of the alkali in the aqueous solution 20 is set to 10 to 50% by weight, and the plant-derived raw material 9 is reacted in this aqueous solution 20, thereby mainly removing the silica component contained in the plant-derived raw material 9 and extracting the silica component into the aqueous solution 20.

[0038] This increases the concentration of organic components and the proportion of carbon in the final carbon material 100. The alkaline aqueous solution 20 is best concentrated at 30% wt, with a pH of about 9 to 14. An aqueous solution 20 produced with potassium hydroxide at a pH of 13 is best. The amount of plant-derived raw material 9 added is best in the range of 80% wtm to 200% wtm, based on the potassium hydroxide before dissolving in water.

[0039] Examples of alkaline materials include sodium hydroxide, potassium carbonate, and alkalis such as potassium hydroxide and sodium carbonate. The best is potassium hydroxide with a pH of 13, which is the same component as potassium contained in the plant-derived raw material 9, and is effective for converting the carbon material 100 into graphene.

[0040] This is a photograph taken through a scanning transmission electron microscope after carbonization at 300 to 500°C without alkali treatment. When checking the element distribution, Al (aluminum) is scattered in the form of fine particles, and K (potassium) is present as large particles.

[0041] Therefore, removing potassium and aluminum improves the purity of the carbon, leading to improved electrical conductivity. It is also ideal for forming porous carbon materials. Aluminum, in particular, dissolves easily in alkalis, so carbonization at high temperatures can remove more of it. Potassium also dissolves easily in alkalis, so it is best to use potassium hydroxide.

[0042] Next, the alkaline plant-derived raw material 9 is subjected to a dehydration treatment (S13) to remove the water content from the aqueous solution 20, and is left in an alkaline atmosphere without being subjected to a neutralization treatment or being washed with water (S13). Because the water content can be removed in this step, it is possible to minimize damage to the apparatus or containers such as crucibles caused by alkaline water due to evaporation of water during carbonization.

[0043] In the dehydration treatment (S13), the plant-derived raw material 9 that has been subjected to the aqueous solution permeation treatment (S12) is placed in a metal, cloth, or plastic dehydration container 15 that has a mesh, slits, or holes, or a combination thereof, and is then dehydrated in a centrifugal dehydrator, similar to laundry. The dehydration container 15 may be any container that allows water to escape by centrifugation, and may be in the shape of a bag, box, cylinder, or the like.

[0044] Another method of dehydration is to place the plant material 9 in a bag-shaped dehydration container 15 and squeeze the bag with a squeezer to remove the water.

[0045] The plant raw material 9 is centrifuged for dehydration in a rotary dehydrator, typically a washing machine (S13). The rotation speed during dehydration is preferably 300 to 3000 rpm, and most preferably 500 to 1500 rpm. This centrifugation can promote the destruction of plant cells and the discharge of impurities such as silica contained in the plant raw material 9.

[0046] Next, a drying process (S14) is carried out in a similar manner, using a drying device or drying in the shade to remove the moisture from the aqueous solution 20. The aqueous solution 20 is left in an alkaline atmosphere without undergoing a neutralization process or washing with water (S14). Because the moisture can be removed in this process, it is possible to minimize damage to the apparatus or containers such as crucibles caused by alkaline moisture due to evaporation of moisture during carbonization. It should be noted that, as long as the alkaline moisture is removed, the drying process (S14) is not necessarily required, and the aqueous solution 20 may be in a wet state, provided that the moisture can be removed in the dehydration process (S13) described above.

[0047] Next, a carbonization process is carried out in which the plant-based raw material 9 is carbonized in an alkaline atmosphere by flowing gas such as nitrogen or argon gas or sealing it with carbon felt or the like, and maintaining a combustion temperature of 1100°C for 5 hours in an oxygen-free environment (S15).

[0048] In the carbonization step (S15), the higher the temperature, the more the graphene formation and graphitization progress. A combustion temperature of approximately 1000°C to 2200°C is best, and it is sufficient to maintain the above temperature for a carbonization time of 2 to 10 hours.

[0049] In addition, while metal is often used for the manufacturing equipment to store the plant-derived raw materials 9, it is preferable to use a rotary kiln-type carbonization device, induction heating furnace, electric furnace, or the like that can withstand alkalinity, such as spraying alumina or using a storage container for storing the plant-derived raw materials 9 made of alumina material to make it resistant to alkalinity.

[0050] Compared to the conventional process of activating the plant-derived raw material 9 by reacting it with a solid alkaline material, the plant-derived raw material 9 in the state of S13 is less likely to cause direct alkali corrosion of metals, which makes it possible to improve the durability of the manufacturing equipment.

[0051] Finally, after the carbonization treatment (S15), the carbon material 100 is subjected to a neutralization treatment (S16) by exposing it to water or an acidic aqueous solution such as hydrochloric acid, sulfuric acid, or citric acid, and further removing any remaining silica, etc. (S16). Furthermore, if the carbon material 100 is then dried and stored in a vacuum, it can be shipped in a state where its physical properties, such as electrical conductivity, are maintained.

[0052] In the neutralization treatment (S16), it is desirable to neutralize by washing using only water such as pure water in order to improve purity. Neutralization using an acid or the like is also good, but it is necessary to wash away the acid and also to remove solids such as silica, so the neutralization treatment (S16) using water is the most cost-effective option.

[0053] 9, pure water 81 is placed in a container 80, and the carbon material 100 and pure water are placed in a bag-shaped permeation membrane 82 that allows only water molecules to pass through, and both ends 83 are submerged in the pure water. A pressure balance occurs from the aqueous solution containing impurities including the carbon material 100, and the water containing alkaline components flows through the membrane into the pure water 81. In this way, the use of the permeation membrane 82 enables rapid treatment.

[0054] Another example of the neutralization treatment (S16) will be described with reference to Fig. 10. An aqueous solution (L1) containing carbon material 100 is forced up by pump 61 from a bathtub 64 containing carbon material 100 and pure water, and passed through tube 62 equipped with a plurality of tubular reverse osmosis membranes 67.

[0055] The aqueous solution (L2) containing the alkaline component is collected from the tube 62 into the collection container 63, and the aqueous solution (L3) containing the carbon material 100 is returned to the bath 64. The bath 64 is replenished with the same amount of pure water as collected in the collection container 63. In this way, the aqueous solution containing the alkaline component is gradually neutralized by circulation.

[0056] <Process Flow 3> A method for producing a carbon material 100 using rice husks, which are one of the plant raw materials 9 of this embodiment, will be described in the examples with reference to Fig. 11. This production method is particularly suitable for carbon material 100 used as a conductive material.

[0057] The plant-based raw material 9 is pulverized. Since microparticulation is performed last, this step requires only pulverization to the extent that the particles penetrate the interior of the plant when immersed in water. Furthermore, since the dehydration step will be performed, the particles should be small enough to not slip through the slits or holes. The optimal size after pulverization is approximately 5 mm to 10 mm. Examples of pulverization methods include mills, mixers, grinders, etc. Furthermore, a specific pulverization step is not necessary; it is sufficient that water or the like penetrates the raw material during washing.

[0058] Next, the crushed plant-based raw material 9 is washed with water (S22). For example, the rice husks are soaked in pure water. After soaking the rice husks for about one hour to one day, stones, mud, etc. are washed away. The liquid temperature is preferably between room temperature and 80°C. The water washing (S22) may be carried out by pouring water and then stirring with a stirrer. Alternatively, washing may be carried out by pouring water little by little while stirring. For stirring, a vortex device or a device that stirs by rotating blades may be used, or a stirrer device may be used.

[0059] Next, the washed plant-derived raw material 9 is placed in the dehydration vessel 15 and dehydrated in a rotary dehydration device such as a washing machine (S23). The rotation speed during dehydration is preferably 300 to 3000 rpm, and most preferably 500 to 1500 rpm.

[0060] The optimum gravitational acceleration during centrifugation by the spin-drying device is approximately 2 G to 5 G. The spin-drying device may be the same device for all steps from washing to rinsing and spin-drying (S22 to S23), or may have a structure in which the spin-drying container 15 is housed or attached.

[0061] Dehydration removes impurities along with the moisture. The plant-based raw material 9 can then be moved to the next baking step while still wet, without going through a drying step. It has been confirmed that this dehydration step by rotation also promotes decomposition of the plant-based raw material 9's tissue, allowing it to proceed to the next step without a drying step.

[0062] Therefore, it became possible to reduce the manufacturing time by eliminating the drying process. Furthermore, when the water is removed by centrifugation during dehydration, the destruction of the cell walls of the plant raw material 9 is promoted, and the destruction reaches further inside.

[0063] Therefore, even in the examples, if rotary dehydration is performed, the drying step is not necessarily required, but drying further reduces the impact of rust, etc. on the combustion equipment. Also, compared to the step of activating the material together with a solid alkaline material, the impact on the combustion equipment is even less.

[0064] Next, in the firing step (S24), the plant-derived raw material 9 is placed in a furnace, which is filled with argon gas or nitrogen gas to create an oxygen-free state, and the temperature inside the furnace is raised to 1100°C and maintained at 1100°C for a fixed period of time of about 1 to 10 hours. Thereafter, the plant-derived raw material 9 is naturally fired for a total firing time of 1 day. This produces the carbon material 10.

[0065] Furthermore, in the baking step (S24), the plant-derived raw material 9 after the dehydration step (S23) is not completely dried, but rather remains slightly moist when it is transferred to the baking step (S24). Therefore, so-called steam activation occurs in the initial stage, which leads to the destruction and decomposition of cell walls.

[0066] Furthermore, steam activation generates micropores, making it easier to form a porous material similar to activated carbon. In the calcination step (S24), it is advisable to use a rotary kiln-type carbonization device, an induction heating furnace, an electric furnace, a continuous carbonization furnace, or the like.

[0067] Furthermore, during the water washing (S22), the plant-derived raw materials 9 are placed in a container such as a pressure cooker, and pressure is applied to the plant-derived raw materials 9 together with water at 2 to 2.45 atmospheres, and a temperature of 120 to 128°C is applied, which quickly destroys the cell walls of the plant-derived raw materials 9, leading to the removal of impurities and an improvement in purity.

[0068] As another example, wheat or barley husks, cocoa husks, and sake lees were burned in an oxygen-free environment at temperatures between 1000°C and 1500°C using a rotary kiln-type carbonization device, induction heating furnace, electric furnace, continuous carbonization furnace, or the like. Alternatively, the burning process may be carried out after steps S21 to S23. For example, in the case of a plant-based raw material 9 such as viscous sake lees, the raw material is stored in a box-shaped storage container with an open top, and pressed from above with a plate-shaped press plate slightly smaller than the open area of ​​the box to compress the raw material. The storage container is then completely filled and the lid is placed. The raw material is then burned at temperatures between 1000°C and 1500°C.

[0069] Further, the specific surface area was measured using the BET adsorption isotherm based on the amount of nitrogen adsorbed at liquid nitrogen temperature.

[0070] As a result, wheat and barley husks, cocoa husks, and sake lees were 15m ２ / g to 80m ２ / g. This small specific surface area improves dispersibility in emulsions such as acrylic, allowing the carbon material to mix evenly and improve conductivity. In addition, the improved dispersibility improves the dispersibility of the coating film, making it possible to ensure strength.

[0071] <Process Flow 4> A method for producing a carbon material 100 using rice husks, which are one of the plant raw materials 9 of this embodiment, will be described in the examples with reference to Fig. 13. This production method is particularly suitable for carbon material 100 used as a conductive material.

[0072] The plant-based raw material 9 is pulverized. Since microparticulation is performed in the final step, it is sufficient to pulverize the raw material to the extent that the particles penetrate the interior of the raw material when immersed in water. Furthermore, since the raw material will undergo a dehydration step, it is sufficient that the particles are small enough not to slip through the slits or holes. The optimal size after pulverization is approximately 5 mm to 10 mm. Examples of pulverization methods include mills, mixers, grinders, etc. Furthermore, a specific pulverization step is not necessary; it is sufficient that the aqueous solution or the like penetrates the raw material during washing, etc.

[0073] Next, the plant-derived raw material 9 is carbonized at a temperature of 500°C to 800°C for about 3 minutes to 3 hours (S32). The carbonized carbide 19 is immersed in acid (S33). Hydrofluoric acid is preferable, and any solution that dissolves silicon components in the acid solution will do.

[0074] Next, after acid washing (S33), the carbide 19 is washed with water or the like to remove the silicon component. At this time, it is best to neutralize the carbide by washing with water or the like. Thereafter, the carbide is immersed in an alkaline aqueous solution as in the above-mentioned process flow 1 or 2 (S34).

[0075] Next, the carbonized material 19 is placed in the dehydration vessel 15 and dehydrated in a rotary dehydration device such as a washing machine (S35). The rotation speed during dehydration is preferably 300 to 3000 rpm, and most preferably 500 to 1500 rpm. When expressed in terms of gravitational acceleration, a rotation speed of about 2 G to 5 G is preferable.

[0076] The dehydrated carbide 19 can be transferred to the next firing step in a wet state without going through a drying step. The silicon component contained in the carbide 19 is removed by this dehydration step (S35) using rotation.

[0077] Therefore, it has become possible to shorten the manufacturing time by eliminating the steps of drying, etc. Furthermore, when the water is removed by centrifugation during dehydration, the destruction of the cell walls of the plant raw material 9 is promoted, allowing the alkaline aqueous solution to penetrate deeper into the plant raw material.

[0078] Therefore, even in the examples, if rotary dehydration is performed, the drying step is not necessarily required, but drying further reduces the impact of rust, etc. on the combustion equipment. Also, compared to the step of activating the material together with a solid alkaline material, the impact on the combustion equipment is even less.

[0079] Next, in the firing step (S35), the plant-derived raw material 9 is placed in a furnace, the furnace is filled with argon gas or nitrogen gas to create an oxygen-free state, the temperature inside the furnace is raised to 1100°C, and the temperature is maintained at 1100°C for a certain period of time, approximately 1 to 10 hours, after which the carbon material 100 is produced.

[0080] Furthermore, in the firing step (S36), the plant-derived raw material 9 after the dehydration step (S35) is not completely dried, but rather remains slightly moist when it is transferred to the firing step (S36). Therefore, so-called steam activation occurs in the initial stage, which leads to destruction of cell walls and promotion of the formation of porous pores.

[0081] In addition to steam activation, activation in an alkaline atmosphere can also generate micropores, making it easier to form a porous material similar to activated carbon. In the calcination step (S36), a rotary kiln-type carbonization device, an induction heating furnace, an electric furnace, a continuous carbonization furnace, or the like can be used. Finally, the neutralization treatment (S16) of process flow 2 may be performed.

[0082] (Graphene and carbide) The carbide 19 obtained in the carbonization step S2 and the firing step (S24, S32) produced in the above example, and the graphene 113 which is the carbon material 100 obtained in the activation step S3 will be described below.

[0083] Fig. 1 shows the Raman spectrum of graphene 113 obtained by the production apparatus of the present invention. Fig. 2 shows the Raman spectrum of carbide 19 obtained by the production apparatus of the present invention. These figures were analyzed using a Raman spectrometer, and the obtained data are Raman spectra with the horizontal axis representing wavelength (wave number (Raman shift (cm-1))) and the vertical axis representing intensity.

[0084] Also, as shown in Table 4, the peak values ​​I G and I D of the G band (2850 cm −1 ) and 2D band (1650 cm −1 ), which are wavelength peaks according to Raman spectroscopy, are given.

[0085] As shown in Table 4, the value obtained by dividing IG by ID is 1.68 for graphene 113, which indicates that it has fewer layers than the plant-derived raw material 9. In particular, it was confirmed that carbide 19 contains a large amount of silicon, and that oxygen functional groups containing -OH, -CHO, -COOH, etc. are generated.

[0086] The value obtained by dividing IG of the graphene 113 by ID is preferably 0.9 or more, and exhibits a value of about 0.9 to 2.0.

[0087] According to thermogravimetry, the ash content of the carbide 19 obtained in the carbonization step S2 is as high as 37.1 wt%, excluding carbon, and silicon (Si) of that ash content accounts for 24 wt% to 50 wt% of the entire carbide 19. In addition, K is 0.51 wt% to 7 wt%, Al is 0.1 wt% to 1.6 wt%, Ca is 0.17 wt% to 0.5 wt%, Fe is 0.4 wt%, and Cr, Ni, Mn, Mg, P, S, and Na are 0.1 wt% or less.

[0088] The carbonized material 19 obtained in the carbonization step S2 without the activation step S3, which is a so-called activation treatment, contains a lot of silicon, and when carbonized in an inert gas, it is not strongly reduced and becomes SiO2-x, which bonds with aromatic -OH groups and the like in the form of -O-Si-O-R to form a lignin polysaccharide complex, which is thought to be likely to take the form of C / SiOx.

[0089] Furthermore, the graphene 113 obtained in the activation step S3 described below has a high ash content excluding carbon, ranging from 1% to 24 wt% according to thermogravimetry, of which silicon (Si) accounts for 1 wt to 20 wt% of the entire graphene 113. In addition, K is 4.3 wt%, Al is 1.5 wt%, Ca is 1.3 wt%, Fe is 0.4 wt%, and P, Mn, Cl, S, and Mg are 0.1 wt% or less.

[0090] As described above, the amount of silicon in the graphene 113 and the carbide 19 that are the carbon material 100 is large, ranging from 1 wt % to 50 wt %.

[0091] As shown in Table 4, the results of the CO 2 adsorption / desorption measurement confirmed that the graphene 113 and the carbide 19 had fine pores with pore diameters mainly ranging from 0.8 nm to 2 nm.

[0092] Therefore, it is considered that they easily adsorb metal ions, etc. Furthermore, as shown in Table 4, the mesopore volumes measured by gas adsorption measurement and water vapor adsorption measurement were 0.487 ml / g for Graphene 113 and 0.259 ml / g for Carbide 19. Furthermore, the micropore volumes were 0.46 ml / g for Graphene 113 and 0.27 ml / g for Carbide 19.

[0093] Furthermore, as shown in Table 4, the particles of graphene 113 or carbide 19 have a diameter distribution of 15 μm to 229 μm, and the median diameter, which is the median value of the integrated value of the distribution, is approximately 110 μm.

[0094] Thus, a mesopore volume of 0.2 ml / g to 0.6 ml / g is formed. In particular, graphene 113 after the activation treatment to remove impurities, which will be described later, shows a higher value, and it is thought that mesopores and micropores grow due to the removal of silicon.

[0095] As shown in Table 4, the specific surface area of ​​graphene 113 measured by the water vapor adsorption measurement method and calculated by the BET method is 1792 m ２ / g, and this width is 890 m ２ / g~2500m ２ / g. Carbide 19 shows 726.4 m2 / g, and this width is 890 m ２ / g~1500m ２ / g. Each of them has a large specific surface area, and the graphene 113 after removing the silicon component (Si) has an even larger specific surface area.

[0096] Therefore, the graphene 113 has a high adsorption effect. In particular, the carbon material 100 produced using rice husks as the plant raw material 9 in process flow 4 has a high adsorption effect of 2000 m ２ / g from 2600m ２ / g value.

[0097] Similarly, carbide 19 may exist in two states: one in which Si (silicon), an elemental component, is contained as minute particles on the surface or inside of carbide 19 in the form of Si (silicon) or silicon dioxide (SiO2), and the other in which Si (silicon) or silicon dioxide (SiO2) is aggregated on the surface or inside of carbide 19. By subjecting carbide 19 to activation treatment, the purity of carbon increases and the specific surface area increases.

[0098] As shown in Table 4, the true densities measured by a gas displacement density measurement device were 2.56 g / cm for graphene 113 and 2.27 g / cm for carbide 19. The bulk density of graphene 113 was 0.21 to 0.29 g / cm.

[0099] Furthermore, the powder resistivity measured by the double ring method and the four-terminal method was 1.27×10 to 5 Ω cm for carbide 19, and 1.0×10 Ω cm for graphene 113 by removing silicon, improving conductivity. Note that the lower the resistance, the better, and the optimum value for graphene 113 is 1.0×10 Ω cm to 3.8×10 Ω cm. Furthermore, by leaving a large amount of silicon in carbide 19, it becomes easier for carbide 19 to dissolve in substances that are easily adsorbed by silicon, and at the same time, its insulating performance is improved.

[0100] (Heat-generating Paint) Hereinafter, a heat-generating paint produced using the above-described carbon material 100 (carbide 19 and graphene 113) as a pigment will be described. The applicant has conducted tests on various types of paint to find the optimal conditions. As the types of paint mentioned in this example, tests were conducted on a solvent-based two-component type, a solvent-based one-component type, and a water-based one-component type.

[0101] As shown in Table 5, the two-component solvent paint uses acrylic urethane as the binder and is diluted with xylene as the solvent. The above-mentioned carbon material 100 (carbide 19 and graphene 113) was used as the pigment. This two-component solvent paint is a type that is cured using a curing agent.

[0102] The solvent-based one-component adhesive used silicone as the binder, xylene as the solvent, and the above-mentioned carbon material 100 (carbide 19 and graphene 113) as the pigment. This solvent-based one-component adhesive is heat-curable and has excellent heat resistance, withstanding temperatures up to 150°C.

[0103] The aqueous one-component type used an acrylic emulsion as the binder, water as the solvent, and the above-mentioned carbon material 100 (carbonized material 19 and graphene 113) as the pigment. The binder was gradually added to the carbon material while stirring with a disperser, and the limiting amount at which the stirred solution remained liquid was determined. The pigment weight concentration (PWC value) at this time was also calculated.

[0104] As shown in Table 6, each carbon material and each coating film with different PWC values ​​were evaluated. First, 10 g of each limit solution was placed on a tin plate, and the binder, hardener, etc. were mixed so that the PWC value within the set < > was achieved. The mixture was then stirred with a spatula to form a coating. The dry film thickness was then measured. The coating film was also visually inspected for irregularities, cracks, color, and gloss spots. ◯ indicates no defects, △ indicates the presence of any of these, and × indicates the presence of noticeable defects.

[0105] The film-forming property is the result of a test in which the coating surface is scratched with a fingernail or the like to see if the coating peels off. ◯ indicates no peeling, and × indicates peeling. The gloss is the result of measuring the 60-degree gloss value. <1 indicates a value less than 1.

[0106] Furthermore, film properties are the results of a test to see if the coating peels off when the coating surface is scratched with a fingernail, etc. A circle indicates no peeling, and an x ​​indicates peeling.

[0107] Flexibility was evaluated by forming a coating film on paper, bending the paper into a mountain fold, and checking whether cracks or breaks occurred in the coating film at the peaks of the folds. ○ indicates that no cracks or breaks occurred, and × indicates that cracks or breaks occurred.

[0108] Next, we will explain its performance as a heat-generating paint. Figure 3 shows the above-mentioned one-component solvent heat-generating paint 50 applied to an insulator 51 such as paper, cloth, or plastic resin. A positive electrode 52 and a negative electrode 53 are provided at the ends of the center of the heat-generating paint 50, and by supplying power to these electrodes, heat is generated from the area where the heat-generating paint 50 is applied. The distance H between the electrodes is 4.5 cm, and the area where the paint is applied is 22.5 cm2.

[0109] 4 and 5 are diagrams showing the heat-generating characteristics of the heat-generating paint 50. Fig. 4 is a graph of time (seconds) and temperature (°C) for a heating element 40 with a coating thickness of 160 μm to 175 μm. V1 is a temperature graph measured at point P in Fig. 3 when DC 20 V is supplied. The power value is 4 to 4.8 W, and the temperature rises from room temperature of 22.1°C to a maximum of approximately 62°C in about 300 seconds.

[0110] V2 is a temperature graph measured at point P in Figure 3 when DC 12V is supplied. The power value is 2 to 2.4W, and the temperature rises from room temperature of 26.3°C to a maximum of approximately 43.4°C in about 300 seconds.

[0111] Figure 5 is a graph of time (seconds) and temperature (°C) for heating element 40 with a coating thickness of 60 μm to 75 μm. V1 is a temperature graph measured at point P in Figure 3 when DC 20 V was supplied. The power value was 1.6 W to 2.0 W, and the temperature rose from room temperature of 25.4°C to a maximum of approximately 44.1°C in approximately 280 seconds.

[0112] V2 is a temperature graph measured at point P in Figure 3 when DC 12V is supplied. The power value is 0.6W, and the temperature rises from room temperature of 25.4°C to a maximum of approximately 32.6°C in about 240 seconds.

[0113] Because the carbon material 100 contains a large amount of silicon, it is possible to improve the strength and electrical resistance of the paint without the need to add an inorganic material later. In particular, a heat-generating paint containing silicon in a carbon material can maintain the continuity of the paint film even when heated to high temperatures, making it possible to produce a planar heater with high heat resistance.

[0114] Furthermore, by mixing the carbide 19 containing many functional groups with the graphene 113 to form a pigment for the paint, it is possible to supply high voltage power such as AC as well as DC while stabilizing the strength.

[0115] Furthermore, the carbide 19 containing many functional groups facilitates dispersion and mixing in the adjustment of the resistance value. The ratio of the carbide 19 to the graphene 113 is preferably about 0.5:9.5 to 3:7. Furthermore, the carbon material 100 having a powder resistance in the range of 1.0×10 Ω cm to 3.8×10 Ω cm may be used alone or in combination with other carbon materials 100.

[0116] Next, another example of the heating element 40 is shown in Figures 12 and 13. Figure 12(A) is a front view of the heating element 40. Figure 12(B) is a cross-sectional view of the heating element 40 taken along line A-B in the front view. The heating paint 50 is made by mixing and kneading a carbon material 100 at a ratio of 10% to 75% by weight into a synthetic resin emulsion, typically vinyl chloride, vinyl acetate, or acrylic. The best ratio is a carbon ratio of 20% to 60% by weight. It may also be dispersed using water.

[0117] The thickness t of the coating film was formed to be 500 μm to 1000 μm. The ideal thickness of the coating film is 100 μm to 1500 μm, and can be changed appropriately depending on the resistance value and the location of use. When an acrylic emulsion was used, it was possible to coat the film with a thick film thickness.

[0118] 12, a heating element 40 has a + electrode 52 and a - electrode 53 formed on wiring 41 using copper foil, silver foil, copper or silver paste, or conductive wire on a substrate 42. The substrate 42 may be glass, ceramic, concrete, cement, cloth (glass fiber, cotton polyester), plastic, etc. Heat-generating paint 50 is applied to the substrate and electrodes and allowed to dry.

[0119] The heating element 40 had a total length of 56 cm, a width of 4 cm, and an electrode width of 1 cm, and the overall resistance between the electrodes was 1 Ω to 20 Ω. When DC 12 V was applied, a temperature rise of 20°C to 80°C from room temperature was confirmed at a power of around 24 W. Here, the carbon material 100 most suitable for heat-generating paint was found to be one in which cocoa husks, barley husks, wheat husks, or the like from among the plant-derived raw materials 9 were burned at a combustion temperature of 900°C to 1500°C.

[0120] 13 has a positive electrode and a negative electrode formed on wiring 41 using copper foil, silver foil, aluminum foil, copper or silver paste, or conductive wire on a substrate 42. The substrate 42 may be glass, ceramic, concrete, cement, cloth (glass fiber, cotton polyester), aluminum tape, plastic, or the like.

[0121] A nonwoven fabric 43 was laid on the substrate 42 and the wiring 41, and then the heat-generating paint 50 was applied thereon and dried. The nonwoven fabric 43 was thin enough to be transparent, and was made of a material that allowed the heat-generating paint 50 to pass through. The thickness of the nonwoven fabric 43 was 10 g / m ２ to 30 g / m ２ is good.

[0122] Various materials such as polyester, polypropylene, polyethylene, rayon, nylon, wool, etc. can be used for the nonwoven fabric 43. The heat-generating paint 50 can pass through the nonwoven fabric 43, so when viewed from the cross section, the nonwoven fabric 43 and the heat-generating paint are mixed together.

[0123] The heating element 40 had a total length of 50 cm, a width of 4 cm, and an electrode width of 1 cm, and the overall resistance between the electrodes was 1 Ω to 20 Ω. When DC 12 V was applied, a temperature rise of 20°C to 90°C from room temperature was confirmed at a power of around 24 W. Here, the carbon material 100 most suitable for heat-generating paint was found to be one in which plant-based raw materials 9 such as cocoa husks, barley husks, and wheat husks were burned at a combustion temperature of 900°C to 1500°C.

[0124] Alternatively, the heat-generating paint 50 may be a paint in which the carbon material 100 is mixed into an aqueous solution in which sodium silicate is diluted with water. This is particularly suitable for carbon materials 100 obtained by carbonizing plant-derived raw materials 9 containing 5% to 20% silicon. The silicon contained in the carbon material 100 dissolves in the sodium silicate, improving conductivity and strength. It is also suitable as a fire-resistant paint, so that when used as a heat-generating paint, it is possible to reduce the risk of fire, etc.

[0125] (Technical Features) Examples of technical features of this embodiment are shown below in parentheses, but are not particularly limiting and are merely examples, and the effects expected from these features will also be described.

[0126] <Feature 1> The method includes a washing step in which the plant-derived raw materials are immersed in an aqueous solution and agitated to wash them with water; a dehydration step in which the plant-derived raw materials are placed in a container after the washing step and rotated in a rotary dehydrator to remove water from the plant-derived raw materials; and a baking step in which the plant-derived raw materials are baked after the dehydration step.

[0127] The aqueous solution may be an alkaline aqueous solution, pure water, treated water, or tap water. The temperature of the aqueous solution is preferably between room temperature (20°C) and 100°C. The dehydration container and the washing container may be the same container. The washing process and the dehydration process may be performed in the same device, such as a washing machine.

[0128] The above features reduce the time required for drying after immersion in a solution or washing with water, as was previously the case, improving production efficiency while also promoting the decomposition of cellulose and other substances, enabling the removal of impurities.

[0129] Regarding industrial applications of the carbon material of the present invention, it can be used as a heat-generating paint for construction such as concrete, heat-generating paint, as well as a conductive paint for battery materials, circuit boards, heat-dissipating materials, etc.

[0130] REFERENCE SIGNS LIST 1 chamber 2 cathode 3 anode 4 high frequency power supply 5 crucible 6 inert gas 7 inlet pipe 8 outlet pipe 9 plant-derived raw material 10 plasma device 14 control valve 15 leak valve 19 carbide 20 control device 21 gas amount control device 30 vacuum pump 40 heating element 42 substrate 50 heat-generating paint 51 insulator 52, 53 electrode 100 carbon material 113 graphene S1 pretreatment process S2 carbonization process S3 activation process.

Claims

1. A method for producing a carbon material, comprising: a washing step of immersing a plant-derived raw material in an aqueous solution and washing it by stirring; a dehydration step of storing the plant-derived raw material in a container after the washing step and rotating it using a rotary dehydrator to remove water contained in the plant-derived raw material; and a firing step of firing the plant-derived raw material in a wet state without drying it after the dehydration step.

2. The method for producing a carbon material according to claim 1, characterized in that the rotation speed of the dehydration device is 300 rpm to 3000 rpm.

3. Powder resistance is 1.0 x 10 －３ Ω cm to 3.8 x 10 －２ The method for producing a carbon material according to claim 1, comprising the step of producing a carbon material having a viscosity of Ω·cm.

4. The plant-based raw materials used are wheat and barley husks, cocoa husks, or sake lees. The carbon material is burned in an oxygen-free environment at a temperature of 1000 to 1500°C and has a specific surface area of ​​15 m. ２ / g to 80m ２ / g.

5. A method for producing a carbon material, comprising: a carbonization process for carbonizing a plant-based raw material; an acid washing process for purifying the carbonized material with an acid solution after the carbonization process; an alkaline aqueous solution immersion process for immersing the carbonized material in an alkaline aqueous solution after the acid washing process; a dehydration process for storing the plant-based raw material in a container and rotating it in a rotary dehydrator to remove water contained in the plant-based raw material; and a firing process for firing the plant-based raw material in a wet state without drying it after the dehydration process.

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