Method for manufacturing graphene

Abstract

The present invention aims to mass-produce graphene at low cost. 【Solution means】 A recovery step of removing the water from a mixture containing water and carbon dioxide and recovering a gas containing the carbon dioxide, and a production step of producing graphene by heating the recovered gas containing carbon dioxide in a quartz container at a temperature of 1700 °C or lower.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing graphene.

Background Art

[0002] There are three conventional methods for generating graphene. The first method is the CVD method that chemically synthesizes from a raw material gas in the gas phase (Patent Document 1). The CVD method is a method in which a carbon precursor is converted into graphene on the catalyst surface. The second method is the Scotch tape method in which graphene is mechanically peeled off from a graphite crystal (Non-Patent Document 1). The Scotch tape method is a method of creating a single-layer (or a small number of layers) of material by attaching and peeling tape to a layered material and repeating the same operation on the remaining part on the tape. The third method is the Hummers method in which graphene is peeled off by oxidation treatment in a liquid phase (Patent Document 2). The Hummers method is a method of synthesizing graphene by oxidizing graphite, preparing oxidized graphite from natural flake graphite, and obtaining reduced graphene oxide by chemical reduction of graphene oxide.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Documents 1 and 2 and Non-Patent Document 1, since it is difficult to mass-produce graphene at low cost, there are problems such that it is not suitable for widespread industrial use. For example, in the CVD method, since a metal catalyst and a transfer process are required, mass production is difficult and the manufacturing cost is high. In the Scotch tape method, since a repetitive operation of attaching a single-layer film to a substrate occurs, it is not suitable for commercial production of graphene. In the Hummers method, since a process of reducing graphene oxide is required, mass production is difficult and the manufacturing cost is high.

[0006] Therefore, an object of the present invention is to mass-produce graphene at low cost.

Means for Solving the Problems

[0007] In order to achieve the object of the present invention, the present invention has the following configuration. That is, a recovery step of removing the water from a mixture containing water and carbon dioxide and recovering a gas containing the carbon dioxide, and a generation step of generating graphene by heating the recovered gas containing carbon dioxide in a quartz container at a temperature of 1700° C. or lower.

Effects of the Invention

[0008] According to the present invention, graphene can be mass-produced at low cost.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential for the invention. Two or more of the plurality of features described in the embodiments may be arbitrarily combined.

[0011] <Method for manufacturing graphene> A method for manufacturing graphene according to an embodiment includes a recovery step of removing water from a mixture containing water and carbon dioxide and recovering a gas containing carbon dioxide, and a production step of generating graphene by heating the recovered gas containing carbon dioxide in a quartz container at a temperature of 1700 ° C or lower. Graphene has electrical conductivity, optical properties, spin transport, and magnetic field effects, and can be used, for example, as an electronic device component.

[0012] <Mixture> The mixture contains water and carbon dioxide. Examples of the mixture include gases discharged from natural gas, thermal power plants, boilers in factories, kilns in cement factories, blast furnaces and converters in steel mills, and incinerators (hereinafter also referred to as exhaust gases). In the method for manufacturing graphene according to an embodiment, water may be directly removed from these mixtures, and then the carbon dioxide-containing gas may be heated in a quartz container to generate graphene. In the method for manufacturing graphene according to another embodiment, these mixtures are once brought into contact with calcium hydroxide to recover carbon dioxide as calcium carbonate, and carbon dioxide is separated from the active ingredient in natural gas or other component gases in the exhaust gas of a power plant or the like. Then, what is obtained by firing the recovered calcium carbonate may be used as the mixture. For the method for manufacturing graphene of the present invention, for convenience of explanation, the method for manufacturing graphene according to another embodiment will be described as an example.

[0013] (Carbon dioxide) Carbon dioxide comes into contact with the aqueous dispersion of calcium hydroxide described below and is recovered as the calcium carbonate described below. Thus, carbon dioxide is processed (consumed) by coming into contact with the aqueous dispersion of calcium hydroxide. Here, the concentration of carbon dioxide according to one embodiment is 5% by volume or more, 10% by volume or more, or 20% by volume or more in natural gas and exhaust gas. Also, the concentration of carbon dioxide is 50% by volume or less, 40% by volume or less, or 30% by volume or less. The range of the concentration of carbon dioxide can be any combination of the above lower limit values and upper limit values.

[0014] <aqueous dispersion of calcium hydroxide> The aqueous dispersion contains water and calcium hydroxide (slaked lime, Ca(OH) 2 ). The aqueous dispersion may further contain acetonitrile (CH 3 CN) for adjusting the absorption rate of carbon dioxide.

[0015] The concentration of calcium hydroxide in the aqueous dispersion containing water and calcium hydroxide is not particularly limited. The concentration of calcium hydroxide is 1% by weight or more, 5% by weight or more, 10% by weight or more, 20% by weight or more, or 30% by weight or more as its solid content. Thereby, the absorption efficiency of carbon dioxide in the aqueous dispersion is improved. Also, the concentration of calcium hydroxide is 80% by weight or less, 70% by weight or less, 60% by weight or less, 50% by weight or less, or 40% by weight or less as its solid content. Thereby, the aqueous dispersion has an appropriate viscosity and the reaction between calcium hydroxide and carbon dioxide becomes uniform. The range of the concentration of calcium hydroxide can be any combination of the above lower limit values and upper limit values. Note that when the aqueous dispersion contains acetonitrile, the concentration of the above calcium hydroxide can be the concentration with respect to the aqueous dispersion containing water, calcium hydroxide, and acetonitrile.

[0016] The concentration of acetonitrile in the aqueous dispersion containing water, calcium hydroxide, and acetonitrile is 1% by weight or more, 5% by weight or more, 10% by weight or more, or 20% by weight or more. Also, the concentration of acetonitrile is 60% by weight or less, 50% by weight or less, 40% by weight or less, or 30% by weight or less. Thereby, it becomes easy to adjust the absorption rate of carbon dioxide in the aqueous dispersion. The range of the concentration of acetonitrile can be any combination of the above lower limit value and upper limit value.

[0017] In one embodiment, the aqueous dispersion is formed by previously preparing a dispersion of water and calcium hydroxide and adding acetonitrile to the dispersion. The dispersion of water and calcium hydroxide can be formed by adding calcium hydroxide or calcium oxide to water. Alternatively, a commercially available dispersion of water and calcium hydroxide can be used as the dispersion of water and calcium hydroxide.

[0018] In one embodiment, calcium hydroxide can be obtained by reacting a calcium salt with an alkali metal hydroxide. Examples of the calcium salt include calcium chloride and calcium sulfate. Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0019] The purity of calcium hydroxide is 80 wt% or more, 90 wt% or more, or 95 wt% or more. Thereby, the absorption efficiency of carbon dioxide in the aqueous dispersion is improved.

[0020] In one embodiment, calcium hydroxide can be in powder form. The average particle size (D50) of calcium hydroxide is 1000 μm or less, 500 μm or less, 100 μm or less, 50 μm or less, or 1 μm or less. Also, the average particle size (D50) of calcium hydroxide is 0.01 μm or more, 0.1 μm or more, 0.5 μm or more, 0.7 μm or more, or 0.9 μm or more. The average particle size (D50) of calcium hydroxide can be any combination of the above lower and upper limit values. By having such an average particle size, the reaction between calcium hydroxide and carbon dioxide is improved. The average particle size (D50) is a value obtained from a volume-based particle size distribution based on the laser diffraction / scattering method, and the D50 value means the particle size (median diameter) at 50% cumulative.

[0021] Water may function as a solvent, for example, tap water, groundwater, distilled water, ion-exchanged water, and the like.

[0022] (Acetonitrile) The purity of acetonitrile is 90% by weight or more, 95% by weight or more, 98% by weight or more, or 99% by weight or more. Thereby, the adjustment of the absorption rate of carbon dioxide in the aqueous dispersion is improved.

[0023] (Additive) The aqueous dispersion can contain, for example, a dispersant as various additives. Examples of the dispersant include dispersants of inorganic compounds and polymer surfactants. Thereby, even when the solid content concentration of calcium hydroxide is high, the dispersibility of calcium hydroxide is improved, and the reaction between calcium hydroxide and carbon dioxide becomes uniform. In one embodiment, the dispersant can uniformly disperse calcium hydroxide by being added to water in advance before adding calcium hydroxide or calcium oxide in the preparation of a dispersion of water and calcium hydroxide, and then adding calcium hydroxide or calcium oxide.

[0024] <Calcium carbonate> By bringing the above carbon dioxide into contact with and reacting it with the aqueous dispersion, calcium carbonate is produced. Calcium carbonate can be recovered by a conventionally known method such as filtration. As described above, the mixture used in the method for producing graphene according to another embodiment is obtained by firing a precipitate of calcium carbonate obtained by reacting calcium hydroxide with carbon dioxide.

[0025] (Firing temperature) The temperature for firing the precipitate of calcium carbonate according to one embodiment is 600 °C or higher, 700 °C or higher, 800 °C or higher, 850 °C or higher, 900 °C or higher, or 950 °C or higher. The temperature for firing the precipitate of calcium carbonate is about 2600 °C (the melting point of calcium oxide) or lower, 1500 °C or lower, 1200 °C or lower, or 1000 °C or lower. The temperature for firing the precipitate of calcium carbonate can be any combination of the above lower limit values and upper limit values. The temperature for firing the precipitate of calcium carbonate according to one embodiment is 600 to 1500 °C. By firing within the above temperature range, calcium carbonate can be sufficiently decomposed into calcium oxide and carbon dioxide.

[0026] (Firing time) The time for firing the precipitate of calcium carbonate is 1 minute or longer, 5 minutes or longer, 10 minutes or longer, 1 hour or longer, 1.5 hours or longer, or 2 hours or longer. The firing time for firing the precipitate of calcium carbonate is 7 hours or shorter, 6 hours or shorter, 5 hours or shorter, 4 hours or shorter, or 3 hours or shorter. The time for firing the precipitate of calcium carbonate can be any combination of the above lower limit values and upper limit values. The time for firing the precipitate of calcium carbonate according to one embodiment is 1 minute to 7 hours. By firing within the above firing time range, calcium carbonate can be sufficiently decomposed into calcium oxide and carbon dioxide.

[0027] <Step of recovering gas containing carbon dioxide> The recovery step according to one embodiment includes removing water from a mixture containing water and carbon dioxide to recover a gas containing carbon dioxide. The recovered gas containing carbon dioxide serves as a raw material for graphene.

[0028] In the recovery process, for example, a method of cooling the mixture and a method using an adsorbent can be used. In the recovery process, the above methods may be used alone or in combination.

[0029] (Method of cooling the mixture) The recovery process according to one embodiment includes removing water by cooling the mixture. The temperature at which the mixture is cooled (at 1 atm) is -78°C or higher, -70°C or higher, -60°C or higher, -50°C or higher, -40°C or higher, or -30°C or higher. The temperature at which the mixture is cooled (at 1 atm) is 100°C or lower, 90°C or lower, 80°C or lower, 70°C or lower, 60°C or lower, 50°C or lower, 40°C or lower, 30°C or lower, 20°C or lower, 10°C or lower, 0°C or lower, -10°C or lower, or -20°C or lower. The range of the temperature at which the mixture is cooled can be any combination of the above lower and upper limit values.

[0030] The temperature at which the mixture is cooled (at 1 atm) according to one embodiment is -78 to 100°C. When it exceeds 0°C, liquid water can be removed from the mixture to recover the gas containing carbon dioxide. When it is 0°C or lower, the water in the mixture can be frozen to recover the gas containing carbon dioxide. When the temperature at which the mixture is cooled is -79°C or lower, the carbon dioxide in the mixture freezes, so the gas containing carbon dioxide cannot be recovered from the mixture. On the other hand, when the temperature at which the mixture is cooled exceeds 100°C, the water in the mixture becomes water vapor, so water cannot be removed from the mixture.

[0031] The temperature at which the mixture is cooled (at 1 atm) according to another embodiment is -78°C to 0°C. In this temperature range, the water in the mixture can be frozen to recover the gas containing carbon dioxide. Since the explanation when the temperature at which the mixture is cooled is -79°C or lower is the same as above, the explanation is omitted.

[0032] As a means for cooling the mixture, for example, one or more heat exchangers can be mentioned. The heat exchanger includes, for example, a metal tube covered with a coolant. Examples of the metal tube include a stainless steel tube and an aluminum tube. Examples of the coolant include dry ice and liquid nitrogen. By passing the mixture through the above heat exchanger, while changing the state of water vapor to water or water to ice, the state of carbon dioxide is not changed. Thereby, water can be removed from the mixture, and a gas containing carbon dioxide can be recovered.

[0033] (Method using an adsorbent) An adsorbent is a substance that absorbs moisture in the air and maintains a dry state. Examples of the adsorbent for removing water from the mixture include silica gel, quicklime, calcium chloride, zeolite, and viscous mineral bentonite. The amount of the adsorbent used may be any amount within the range capable of removing water from the mixture. Also, by leaving the mixture in the presence of the adsorbent, the adsorbent absorbs water in the mixture while not absorbing carbon dioxide. Thereby, water can be removed from the mixture, and a gas containing carbon dioxide can be recovered. Note that the method using an adsorbent has an advantage that temperature control of the mixture does not need to be performed.

[0034] (Graphene production process) The production process includes generating graphene by heating the recovered gas containing carbon dioxide in a quartz container at a temperature of 1700 °C or lower.

[0035] (Container) The container for introducing the recovered gas containing carbon dioxide is preferably a cylindrical quartz container from the viewpoints of heat resistance, light transmittance, and chemical resistance to high heating temperatures. The quartz container is made of silicon dioxide (SiO 2It is a quartz glass container made from and contains almost no metal impurities. Examples of quartz glass include fused quartz and synthetic quartz. Fused quartz is produced from quartz powder obtained by melting and refining natural quartz crystals. Synthetic quartz is chemically synthesized using ultra-high purity silicon tetrachloride and has a higher purity than fused quartz. For example, the purity of synthetic quartz is 99.99% or more. Quartz glass has a simple and strong molecular structure and has the property of being less likely to undergo thermal deformation. Therefore, the softening point of the quartz container is, for example, 1700°C. Quartz glass, which has excellent properties in various physical characteristics, is used in various fields such as optical fibers, optical filters, laboratory physicochemical equipment, optical lenses, and incinerator viewing windows. Here, in the conventional CVD method, a metal foil substrate is generally used. Therefore, in order to generate graphene without changing the surface shape of the metal foil substrate and without causing evaporation of the metal foil, it is necessary to perform plasma treatment at a temperature sufficiently lower than the melting point of the metal catalyst. For example, in the case of a copper foil substrate where a metal catalyst is generally used in the production of graphene, it is necessary to perform the treatment at a temperature sufficiently lower than the melting point of copper (1080°C). On the other hand, since the softening point of the quartz container according to the present invention is about 1700°C, the present invention can produce graphene at a heating temperature higher than the CVD method. Thus, since the present invention has the advantage of being able to produce graphene in a wider temperature range (for example, 1000°C or higher) than the CVD method, it is possible to realize mass production of graphene in, for example, a commercial plant.

[0036] The shape of the container according to one embodiment is, for example, cylindrical, linear, curved (such as U-shaped, V-shaped, etc.), or a combination of these shapes. The container according to one embodiment is a closed reactor that confines the introduced carbon dioxide, but is not limited thereto. For example, the container may be a flow reactor. A flow reactor refers to a device that continuously supplies a raw material for graphene (i.e., a gas containing recovered carbon dioxide) from one end of the reactor and continuously extracts graphene from the other end of the reactor. When the container is a flow reactor, a pressure pump, a temperature sensor, a pressure sensor, a cooling water tank, a pressure regulating valve, and a graphene recovery container can be optionally provided. When the container is a flow reactor, the production time of graphene can be shortened compared to a closed reactor, enabling mass production of graphene.

[0037] (Heating temperature) The temperature for heating a gas containing carbon dioxide in a quartz container according to one embodiment is 1700 °C or lower, 1600 °C or lower, or 1500 °C or lower. The temperature for heating carbon dioxide in the quartz container is 1000 °C or higher, 1100 °C or higher, or 1200 °C or higher. The range of the temperature for heating a gas containing carbon dioxide in the quartz container can be any combination of the above lower limit values and upper limit values. Thereby, graphene can be efficiently produced.

[0038] (Heating time) The time for heating a gas containing carbon dioxide in a quartz container according to one embodiment is 5 minutes or more, 10 minutes or more, or 15 minutes or more. The time for heating a gas containing carbon dioxide in the quartz container is 3 hours or less, 2 hours or less, or 1 hour or less. The time for heating a gas containing carbon dioxide in the quartz container can be any combination of the above lower limit values and upper limit values. The time for heating a gas containing carbon dioxide in a quartz container according to one embodiment is 5 minutes to 1 hour. Thereby, graphene can be efficiently produced.

[0039] (Atmosphere) The atmosphere inside the quartz container according to one embodiment is an inert gas or a vacuum. Examples of the atmosphere inside the quartz container during heating include inert gases such as nitrogen, argon, and helium, or a vacuum. By generating graphene in an oxygen-free environment, graphene with few oxygen functional groups can be obtained, so the reduction process of graphene can be omitted. Note that heat treatment in an atmosphere where oxygen exists, such as in air, is not preferable because ablation of graphite occurs.

[0040] When the inside of the quartz container is a vacuum, the pressure is 1 Pa or more, 5 Pa or more, 10 Pa or more, or 20 Pa or more. Also, the pressure is 200 Pa or less, 180 Pa or less, 160 Pa or less, or 140 Pa or less. The pressure range can be any combination of the above lower limit values and upper limit values. By generating graphene in an environment with little oxygen, graphene with few oxygen functional groups can be obtained, so the reduction process of graphene can be omitted.

[0041] (Catalyst) The generation process according to one embodiment includes heating the gas containing the recovered carbon dioxide in a quartz container without using a catalyst. Examples of the catalyst include metal catalysts of noble metals such as nickel, copper, cobalt, iridium, and platinum. The growth of single-layer graphene by CVD method is generally carried out on a copper foil. However, in the CVD method using a metal catalyst, since it is necessary to transfer graphene onto an insulating substrate, an increase in cost occurs due to processes such as the etching process and transfer process of the metal catalyst. Also, due to geopolitical risks and constraints on buried resources, the price of metal catalysts is prone to soar. Therefore, the market needs for a method of manufacturing graphene without using a metal catalyst, which leads to a reduction in the cost of graphene production, are increasing even more. The present invention can generate graphene in a quartz container that is industrially widely used without using a metal catalyst in the generation process, so it is an excellent invention that can sufficiently meet the market needs such as realizing a reduction in the cost of graphene production.

[0042] Hereinafter, embodiments of the present invention will be described by way of examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example

[0043] (Example 1) 7.418 g of calcium hydroxide and water (a predetermined amount) were put into a container and mixed. Natural gas (CO 2 concentration of 10.00%) was introduced into the container for 5 minutes. CO 2 concentration (volume %) represents the concentration of CO 2 in natural gas. Natural gas contains methane, ethane, nitrogen, butane, etc. in addition to CO 2 . After 5 minutes, the introduction of natural gas into the container was stopped. By allowing the container to stand for 5 minutes, a precipitate of calcium carbonate was obtained. The gas in the container was sampled and gas analysis was performed to confirm that the amount of CO 2 treated (consumed) from natural gas was 99.99%. The precipitate of calcium carbonate was put into a large electric furnace at 840 °C and calcined for 10 minutes. A mixture containing carbon dioxide and water separated from calcium carbonate was collected from the gas supply port at the upper part of the large electric furnace. By passing the mixture through a heat exchanger (specifically, a stainless steel tube covered with dry ice around it), water was removed and a gas containing carbon dioxide was recovered. The gas containing the recovered carbon dioxide was confined in a quartz tube that had been evacuated in advance in a large electric furnace for 5 minutes and then heated at 1500 °C for 20 minutes. 1.187 g of graphene was generated and deposited inside the quartz tube. The chemical bonding state of the generated graphene was measured by X-ray photoelectron spectroscopy (XPS).

[0044] (Example 2) Only the differences from Example 1 will be described. In Example 2, the amount of calcium hydroxide was 3.709 g, the CO 2 concentration in natural gas was 5.00%, the introduction time of natural gas was 2.5 minutes, the heating time of the gas containing the recovered carbon dioxide was 10 minutes, and the amount of graphene generated was 0.579 g. Otherwise, since graphene was generated in the same manufacturing process as in Example 1, detailed description is omitted.

[0045] (Analysis Method of Graphene) To analyze the chemical bonding states of the graphene obtained in Example 1 and Example 2 and the comparative example (commercial graphite), X-ray photoelectron spectroscopy (X-ray source: monochromatized Al Kα ray) was used.

[0046] Figure 1 is a diagram showing the XPS analysis results of the graphene of Example 1 and Example 2 and the comparative example (commercial graphite).

[0047] In Example 1 (curve 101) and Example 2 (dashed line 102) of Figure 1, when the binding energy (horizontal axis, Binding energy) was between 284 and 285, a peak in the intensity of the emitted photoelectrons (vertical axis) was significantly confirmed, and the intensity of the emitted photoelectrons exceeded 5.0. On the other hand, in the comparative example (curve 103), a slight peak in the intensity of the emitted photoelectrons was confirmed when the binding energy was 283, but the intensity of the emitted photoelectrons decreased after the binding energy reached 283.

[0048] According to the analysis results in Figure 1, it was found that the intensity of the emitted photoelectrons in Example 1 and Example 2 was about 20 times or more higher than that in the comparative example (commercial graphite). Thus, it was confirmed that graphene was produced by removing water from the mixture and heating the recovered gas containing carbon dioxide in a quartz tube at 1500°C.

[0049] As described above, the present invention has a remarkable effect that graphene can be mass-produced at a low cost compared with the prior art.

[0050] The invention is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the invention.

Explanation of Reference Numerals

[0051] 101 Curve 102 Dashed line 103 Curve

Claims

1. A recovery step of removing the water from a mixture containing water and carbon dioxide to recover a gas containing the carbon dioxide; and a generating step of generating graphene by heating the collected carbon dioxide-containing gas in a quartz container at a temperature of 1700° C. or less. How graphene is produced.

2. The recovering step comprises removing the water by cooling the mixture. The method of claim 1 .

3. The temperature to which the mixture is cooled (at 1 atmosphere) is −78 to 100° C. The method according to claim 2 .

4. The generating step includes heating the recovered gas containing carbon dioxide in the quartz vessel without using a catalyst. The method of claim 1 .

5. The time for heating the recovered carbon dioxide-containing gas in the quartz vessel is 5 minutes to 1 hour. The method of claim 1 .

6. The atmosphere in the quartz container is an inert gas or a vacuum. The method of claim 1 .

7. The mixture is obtained by calcining a precipitate of calcium carbonate obtained by reacting calcium hydroxide with carbon dioxide. The method of claim 1 .

8. The temperature for calcining the calcium carbonate precipitate is 600 to 1500°C. The method of claim 7.

9. The time for calcining the calcium carbonate precipitate is 1 minute to 7 hours. The method of claim 7.

Images