Method for producing porous carbon

Abstract

To provide a method for producing porous carbon capable of stably producing porous carbon rich in gas adsorption.SOLUTION: One aspect of the method for producing porous carbon according to the present invention comprises a step of dissolving a carbon raw material in a good solvent thereof, a step of mixing a solution obtained in the dissolving step with a poor solvent of the carbon raw material, and a step of separating deposited solid components from the mixed liquid obtained in the mixing step. The yield of the carbon raw material is 35 mass% or more at heating up to 1000°C under an inert atmosphere.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing porous carbon. [Background technology]

[0002] In recent years, carbon dioxide is thought to have a large impact on global warming. Carbon dioxide adsorption technology using carbon materials has attracted attention as an effective measure against this global warming problem. Porous carbon, which has pores on the surface with a diameter on the order of nanometers and a high specific surface area, is useful as an adsorbent. The poor solvent method is known as a method for producing such porous carbon (JP Patent Publication No. 2021-038127). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-038127 Summary of the Invention [Problem to be solved by the invention]

[0004] In the method for producing porous carbon described in the above publication, a carbon raw material is mixed with a good solvent and a poor solvent, and the solid matter precipitated from this mixed liquid is carbonized in a solid phase to obtain porous carbon having a high bulk density and a large specific surface area per unit volume. In the above production method, raw materials with a relatively high oxygen content, such as lignite and woody biomass extracts, often have high solubility in the solvent used in the poor solvent method, so there is a risk that the solid matter cannot be sufficiently precipitated. There is a demand for stable production of suitable porous carbon from a variety of raw materials.

[0005] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing porous carbon, which is capable of stably producing porous carbon having excellent gas adsorption properties. [Means for solving the problem]

[0006] One embodiment of the method for producing porous carbon of the present invention includes a step of dissolving a carbon raw material in a good solvent, a step of mixing the solution obtained in the dissolving step with a poor solvent for the carbon raw material, and a step of separating the solid matter precipitated from the mixed liquid obtained in the mixing step, and the yield of the carbon raw material is 35 mass% or more when heated up to 1000°C in an inert atmosphere. Effect of the Invention

[0007] The method for producing porous carbon of the present invention can stably produce porous carbon with excellent gas adsorption properties. The present invention can obtain porous carbon capable of efficiently absorbing carbon dioxide from a variety of raw materials. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a flow diagram showing a method for producing porous carbon according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a graph showing the relationship between the temperature and the mass of the carbon raw material when the carbon raw material was heated at 10° C. / min in a nitrogen atmosphere. [Diagram 3] FIG. 3 is a graph showing the relationship between the temperature and the mass reduction rate of the carbon raw material when the carbon raw material was heated at a rate of 10° C. / min in a nitrogen atmosphere. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Description of the embodiment of the present invention] First, the embodiments of the present invention will be listed and described.

[0010] One embodiment of the method for producing porous carbon of the present invention includes a step of dissolving a carbon raw material in a good solvent, a step of mixing the solution obtained in the dissolving step with a poor solvent for the carbon raw material, and a step of separating the solid matter precipitated from the mixed liquid obtained in the mixing step, and the yield of the carbon raw material is 35 mass% or more when heated to 1000°C at a heating rate of 10°C / min in an inert atmosphere.

[0011] The method for producing porous carbon (hereinafter also referred to as "the production method") uses a carbon raw material that has a yield of 35 mass% or more when heated to 1000°C at a heating rate of 10°C / min in an inert atmosphere. Therefore, it is possible to stably produce porous carbon with excellent gas adsorption properties from various types of carbon raw materials and reduce production costs.

[0012] The yield may be 70% by mass or less. When the yield is 70% by mass or less, the porous carbon can be obtained more stably.

[0013] The method may further include a step of removing low boiling point components from the carbon raw material before the dissolving step. By removing the low boiling point components before dissolving the carbon raw material, porous carbon can be obtained more stably.

[0014] The carbon raw material may contain 1% by mass or less of a component having a boiling point of 250° C. or less. By doing so, it is possible to obtain porous carbon more stably.

[0015] The method may further include a step of solid-state carbonizing the solid fraction separated in the separating step. That is, by solid-state carbonizing the solid fraction, porous carbon having excellent gas adsorption properties is obtained.

[0016] Note that a "good solvent for a carbon raw material" refers to a solvent in which the solubility of the carbon raw material is 5% by mass or more at 25°C, and a "poor solvent for a carbon raw material" refers to a solvent in which the solubility of the carbon raw material is less than 5% by mass at 25°C.

[0017] [Details of the embodiment of the present invention] An embodiment of the present invention will be described in detail below.

[0018] As shown in Fig. 1, the method for producing porous carbon of the present invention includes a step S2 of dissolving a carbon raw material in a good solvent, a step S3 of mixing the solution obtained in the dissolving step S2 with a poor solvent for the carbon raw material, and a step S4 of separating the solid matter precipitated from the mixed solution obtained in the mixing step S3. The production method further includes a step S5 of solid-phase carbonization of the solid matter separated in the separating step S4. Furthermore, the production method of this embodiment includes a step S1 of removing low-boiling point components of the carbon raw material before the dissolving step S2.

[0019] In this manufacturing method, the carbon raw material is solidified without going through a melt. Therefore, a porous body can be obtained as a solid content from various carbon raw materials as long as the yield is 35 mass% or more when heated to 1000°C in an inert atmosphere, and by solid-phase carbonization of this solid content, porous carbon with excellent gas adsorption properties can be produced at low manufacturing costs. In addition, the porous carbon produced by this manufacturing method has a high proportion of micropores, which are pores with a diameter of less than 2 nm.

[0020] The lower limit of the heating rate for heating the carbon raw material to 1000° C. is not particularly limited, and may be, for example, 5° C. / min or 10° C. / min. The upper limit of the heating rate is not particularly limited, and may be, for example, 20° C. / min or 15° C. / min. By setting the heating rate within the above range, heating can be performed efficiently, and the accuracy of the evaluation of the heated carbon raw material can be improved.

[0021] [Removal step] In the removing step S1, low boiling point components of the carbon raw material are removed. The means for removing the low boiling point components are not particularly limited, and examples thereof include a heating method, a distillation method, and a solvent extraction method. If the carbon raw material contains a large amount of low boiling point components, which are components with small molecular weights, the solubility in a good solvent described below becomes excessively high, and there is a risk that the amount of solid matter precipitated in the separating step S4 will be insufficient. For this reason, it is preferable to remove the low boiling point components before dissolving the carbon raw material in a good solvent.

[0022] The carbon raw material used has a yield of 35% by mass or more when heated to 1000° C. under an inert atmosphere. The carbon raw material is not particularly limited as long as it satisfies the above yield, and examples of the carbon raw material include carbon materials that are graphitized when heat-treated at high temperatures of 2500° C. or more under normal pressure, such as high-grade coal such as bituminous coal, coal pitch, petroleum asphalt, and ashless coal. Alternatively, the carbon raw material may be an extract of low-grade coal such as subbituminous coal or lignite, or biomass such as broad-leaved trees, coniferous trees, and herbaceous plants.

[0023] If the yield is less than the lower limit, the solubility of the carbon raw material in the good solvent becomes too high, and the precipitate becomes pasty, which may make it difficult to carry out the subsequent steps.

[0024] The upper limit of the yield is preferably 70% by mass, more preferably 65% ​​by mass. If the yield exceeds the upper limit, the solubility of the carbon raw material in the good solvent is not high, and as a result, a large amount of solvent may be required.

[0025] The inert atmosphere is not particularly limited, and examples thereof include nitrogen and argon, with nitrogen being preferred from an economical viewpoint.

[0026] The coal used as the raw material for the ashless coal is not particularly limited, and examples thereof include bituminous coal, which has a high extraction rate of ashless coal, and less expensive low-grade coal (subbituminous coal and lignite). When low-grade coal is used as the raw material, the lower limit of the carbon content is preferably 65% ​​by mass. On the other hand, the upper limit of the carbon content is preferably 85% by mass, and more preferably 82% by mass. By setting the carbon content within the above range, the elution rate of the solvent-soluble component can be made sufficient, and the cost of the raw material can be prevented from increasing.

[0027] Ashless coal as the carbon raw material may be used alone, or a carbon raw material other than ashless coal may contain ashless coal. In general, compared with coal pitch obtained through carbonization and distillation of coal performed at 1000°C or higher, ashless coal obtained by extraction from coal at 400°C or lower contains a large amount of heteroatoms such as oxygen and is less likely to form a layered structure. For this reason, by including ashless coal in the carbon raw material, porous carbon with a large specific surface area per unit volume can be obtained relatively easily. In addition, since ashless coal has a large heteroatom content and a large molecular weight, the yield in the solid-phase carbonization step S5 described later can be improved.

[0028] The upper limit of the content of components having a boiling point of 250° C. or less in the carbon raw material is preferably 1 mass %, and more preferably undetectable (below the limit of detection performance of the detector). By keeping the content of components having a boiling point of 250° C. or less below the upper limit, excessive affinity to the good solvent can be further reduced, and the stability of the production of porous carbon can be further improved.

[0029] The carbon raw material preferably contains oxygen at 12%-daf (dry ash free) or more. When the carbon raw material contains oxygen at 12%-daf or more, micropores are easily formed in the resulting porous carbon.

[0030] [Dissolving step] In the dissolving step S2, the carbon raw material is dissolved in the good solvent. The good solvent is not particularly limited as long as it can dissolve the carbon raw material, but it is preferable that the good solvent contains a nitrogen-containing compound. By making the good solvent contain a nitrogen-containing compound in this way, the solubility of the carbon raw material can be increased.

[0031] The nitrogen-containing compound is, for example, pyridine (C 5 H 5 N), quinoline (C 9 H 7 N), N-methylpyrrolidone (C 5 H 9Among them, pyridine is preferred because it has a high dissolving power and a relatively low boiling point, making it easy to handle.

[0032] The lower limit of the content of the carbon raw material in the solution after dissolution is preferably 5% by mass, more preferably 10% by mass. Meanwhile, the upper limit of the content of the carbon raw material is preferably 50% by mass, more preferably 40% by mass. By setting the content of the carbon raw material within the above range, it is possible to reduce the amount of undissolved carbon raw material and improve the stability of the production of porous carbon.

[0033] [Mixing step] In the mixing step S3, the solution obtained in the dissolving step S2 is mixed with a poor solvent for the carbon raw material.

[0034] The poor solvent is not particularly limited as long as it has a low solubility for the graphitizable carbon raw material, but is preferably one that mixes well with the good solvent. It is also preferable that the poor solvent does not contain a nitrogen-containing compound. By not including a nitrogen-containing compound in the poor solvent in this way, the precipitation efficiency of the solid content can be increased. Furthermore, by using a combination in which the good solvent contains a nitrogen-containing compound and the poor solvent does not contain a nitrogen-containing compound, the production efficiency of the porous carbon can be improved.

[0035] The poor solvent is water (H 2 O), methanol (CH 4 O), ethanol (C 2 H 6 O), acetone (C 3 H 6 O), toluene (C 7 H 8 ), hexane (C 6 H 14) and the like. When a highly polar nitrogen-containing compound is used as the good solvent, the poor solvent is preferably one having high polarity that contains oxygen and is easily mixed with the good solvent. Examples of such poor solvents include water, methanol, ethanol, and acetone. When methylnaphthalene or the like is used as the good solvent, the poor solvent is preferably toluene or hexane, which has a sufficiently smaller dissolving power for carbon raw materials than methylnaphthalene or the like.

[0036] The method for mixing the solution and the poor solvent is not particularly limited, but a method of adding the solution to the poor solvent is preferred. By adding the carbon raw material dissolved in the good solvent to a large amount of poor solvent, the carbon raw material instantly becomes a powdery solid content, thereby further improving the production efficiency of porous carbon.

[0037] The lower limit of the mass ratio of the poor solvent to the solution is preferably 3, more preferably 5. Meanwhile, the upper limit of the mass ratio is preferably 20, more preferably 10. By setting the mass ratio within the above range, the carbon raw material can be appropriately precipitated, the yield of the porous carbon can be improved, and the production efficiency of the porous carbon can be further improved.

[0038] [Separation step] In the separation step S4, the precipitated solids are separated from the mixed solution obtained in the mixing step S3. Specifically, as described above, when the solution and the solvent are mixed, the precipitated solids are precipitated, and the precipitated solids are separated, for example, by filtration. The separated solids are preferably further dried under reduced pressure.

[0039] The majority of the pores formed in the precipitated solid are micropores with a diameter of less than 2 nm, and mesopores with a diameter of 2 nm or more and less than 50 nm are relatively few.

[0040] This production method is a so-called poor solvent method, and therefore does not require special equipment or the like, making it possible to easily produce porous carbon, and thus to reduce production costs.

[0041] [Solid-phase carbonization process] In the solid-phase carbonization step S5, the solid content separated in the separation step S4 is solid-phase carbonized. Specifically, the solid content is infusible and heated in this order to obtain porous carbon.

[0042] <Infusible treatment> In the solid-phase carbonization step S5, the solid content is infusible. This infusible treatment can suppress undesirable melting (liquid-phase carbonization) during the carbonization process by the subsequent heat treatment, making it possible to carbonize in the solid phase. Infusible treatment is performed, for example, by heating in an oxygen-containing atmosphere using a known heating furnace. The oxygen-containing atmosphere may be, for example, air.

[0043] The lower limit of the heating temperature (infusibility treatment temperature) when infusibility is performed is preferably 150°C, more preferably 180°C. On the other hand, the upper limit of the infusibility treatment temperature is preferably 300°C, more preferably 280°C. By setting the infusibility treatment temperature within the above range, it is possible to sufficiently promote infusibility while suppressing the melting of the solid content before infusibility. In addition, it is possible to suppress inefficiency due to a long infusibility treatment time. The heating rate for reaching the infusibility treatment temperature can be, for example, 0.01°C / min or more and 10°C / min or less.

[0044] In addition, the lower limit of the stabilization treatment time when stabilization is performed is preferably 10 minutes, more preferably 20 minutes. On the other hand, the upper limit of the stabilization treatment time is preferably 120 minutes, more preferably 90 minutes. If the stabilization treatment time is less than the lower limit, the stabilization may be insufficient. Conversely, if the stabilization treatment time exceeds the upper limit, the manufacturing cost of the porous carbon may increase unnecessarily.

[0045] <Heat treatment> After the infusibility treatment, a heat treatment is performed. This heat treatment is performed in a heating section. The heating section carbonizes the solid content by heating while substantially maintaining its aggregated state (solid-phase carbonization). As the heating section, for example, a known electric furnace or the like can be used. The low-crystalline solid content is inserted into the heating section, the inside is replaced with an inert gas, and then the solid content is heated while blowing the inert gas into the heating section, thereby achieving solid-phase carbonization of the solid content. The inert gas is not particularly limited, but examples thereof include nitrogen and argon. Among these, inexpensive nitrogen is preferable.

[0046] The lower limit of the heating temperature in the heating section is preferably 600°C or higher, more preferably 900°C. Meanwhile, the upper limit of the heating temperature is preferably 1300°C, more preferably 1100°C. By setting the heating temperature within the above range, carbonization and pore development can be sufficiently promoted, and the specific surface area (porosity) can be made suitable, thereby improving the heat resistance of the equipment and reducing the manufacturing cost in terms of fuel consumption. The heating rate for reaching the above heating temperature can be, for example, 0.01°C / min or higher and 10°C / min or lower.

[0047] The lower limit of the heating time is preferably 10 minutes, more preferably 20 minutes. Meanwhile, the upper limit of the heating time is preferably 10 hours, more preferably 8 hours. By setting the heating time within the above range, carbonization can be sufficiently promoted, and a decrease in the production efficiency of the porous carbon can be suppressed.

[0048] <Activation treatment> In this production method, porous carbon in which the majority of the pores are micropores can be obtained without performing an activation treatment, but an activation treatment may be performed. By performing an activation treatment, the number of micropores can be further increased. The activation treatment may be a mild one.

[0049] The activation treatment can be carried out by a known method. For example, after the heat treatment or simultaneously with the heat treatment, CO 2 The surface of the solid was partially gasified using an inert gas containing (C+CO2 →2CO) 2 Activation can be used.

[0050] CO in the above inert gas 2 The lower limit of the concentration is not particularly limited, but is preferably 10 mass %. 2 The upper limit of the concentration is not particularly limited, but is preferably 100 mass% (pure CO 2 ) may be used. 2 By setting the concentration within the above range, it is possible to obtain the desired activation effect while suppressing a decrease in production efficiency due to long-term treatment.

[0051] CO 2 The weight loss of the porous carbon due to activation was 2 It is preferable that the weight loss is 105% by mass or more and 150% by mass or less with respect to the weight loss when the carbonization treatment is performed in an inert gas that does not contain . By setting the weight loss within the above range, the activation effect (porosity) can be sufficiently promoted.

[0052] [Porous carbon] The characteristics of the porous carbon obtained by this production method will be described below.

[0053] The porous carbon is particulate and has many pores with an average diameter of, for example, 0.5 nm to 2 nm. The porous carbon can be suitably used as a gas adsorbent for oxygen, hydrogen, carbon dioxide, etc., an adsorbent for water treatment, an electrode for EDLC (Electrical Double Layer Capacitor), etc. The "average diameter" refers to a pore size distribution measured by a gas adsorption method.

[0054] <Advantages>

[0055] In this manufacturing method, a carbon raw material that has a yield of 35% by mass or more when heated to 1000°C under an inert atmosphere is used as the raw material. Therefore, porous carbon with excellent gas adsorption properties can be stably obtained from various types of carbon raw materials. In addition, in this manufacturing method, the carbon raw material is solidified without going through a melt, so a solid content of a porous body is obtained. Therefore, by solid-phase carbonization of this solid content, porous carbon can be obtained at low manufacturing costs. In addition, the porous carbon manufactured by this manufacturing method has a high proportion of micropores, which are pores with a diameter of less than 2 nm.

[0056] [Other embodiments] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims. EXAMPLES

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] [Example 1] As carbon raw materials, ashless coal produced by solvent extraction of coal and extracts of coniferous and broadleaf trees were prepared. Pyridine (C 5 H 5 N, boiling point 115°C) was prepared, and each carbon raw material was dissolved in this good solvent to obtain a solution. The content of each carbon raw material in this solution was adjusted to 20 mass % by stirring. 100 g of this solution was mixed with 2.0 L of water prepared as a poor solvent, and the presence or absence of precipitation of solids (powder) was confirmed. Table 1 shows the carbon yield when each carbon raw material was heated to 1000 °C at a heating rate of 10 °C / min in an inert atmosphere, the oxygen content of each carbon raw material, whether or not solid matter was precipitated, and the carbon dioxide (CO) emission based on the mass of the obtained porous carbon. 2 ) and the amount of adsorption.

[0059] The amount of carbon dioxide adsorption was determined as the equilibrium adsorption amount of carbon dioxide at an equilibrium adsorption pressure of 0.4 MPa and 0°C by the following constant volume method. (1) A first container and a second container having an internal volume larger than that of the first container and connected to the first container via a connecting pipe were prepared. (2) 1.0 g of porous carbon (sample) was placed in the first container, and the first container was heated to 200° C. to degas the first container and the second container under reduced pressure, and the sample was dried. (3) The valve provided on the connecting tube was closed, and the dried sample was sealed in the first container under reduced pressure. (4) After introducing carbon dioxide at a predetermined pressure (e.g., 0.9 MPa) into the second container, the valve was opened to allow the sample to adsorb the carbon dioxide. After 60 minutes, the internal pressures of the first container and the second container were measured and regarded as the equilibrium adsorption pressure. (5) When the equilibrium adsorption pressure was 0.4 MPa or less, the above steps (3) and (4) were repeated until the equilibrium adsorption pressure reached 0.4 MPa or more. (6) An adsorption isotherm was created from the amount of carbon dioxide adsorbed by the carbon raw material when the equilibrium adsorption pressure was 0.4 MPa, and the equilibrium amount of carbon dioxide adsorbed by the above sample at 0.4 MPa was calculated.

[0060] [Table 1]

[0061] In Table 1, "A" in the column for solid matter precipitation indicates that a powdery solid matter was precipitated. In other words, it indicates a carbon raw material that is suitable for the production method (poor solvent method). "B" indicates that the carbon raw material did not dissolve at 20 mass% in the good solvent. "C" indicates that no powdery solid matter was precipitated, and the carbon raw material was dissolved in the good solvent to form a paste. Carbon raw materials with "B" and "C" are considered to be unsuitable for the production method. CO 2 The "-" in the column for the amount of adsorption indicates that powdered carbon was not obtained, and therefore CO 2 This indicates that the amount of adsorption was not measured.

[0062] Among carbonaceous materials with high oxygen content, low boiling point components are considered to have high solubility in good solvents. A coniferous extract was selected as a carbonaceous material with high oxygen content, and a comparison was made between a coniferous extract extracted at 350°C (Test Example 9-1) and a product obtained by removing low boiling point components below 250°C from this extract (Test Example 9-2), and between a coniferous extract extracted at 330°C (Test Example 10-1) and a product obtained by removing low boiling point components below 250°C from this extract (Test Example 10-2). The removal of low boiling point components below 250°C was performed by heating at 240°C and 1 mmHg or less in a vacuum dryer. In Test Example 9-2, 10% by mass of the low boiling point components could be removed compared to Test Example 9-1, and in Test Example 10-2, 13% by mass of the low boiling point components could be removed compared to Test Example 10-1. The weight changes when these carbonaceous materials were heated at 10°C / min in a nitrogen atmosphere are shown in Figures 2 and 3. 2 and 3, the horizontal axis indicates the temperature when the carbon raw material is heated at 10°C / min in a nitrogen atmosphere, and the vertical axis indicates the mass of the carbon raw material and the rate of mass reduction of the carbon raw material. The carbon dioxide absorption increased when the low boiling point components below 250°C were removed (Test Examples 9-2 and 10-2). The results are shown in Table 2.

[0063] [Table 2]

[0064] It can be seen from Table 2 that the oxygen content of the carbon raw material from which the low boiling point components were removed remains almost unchanged. On the other hand, it can be seen from Table 2 that the amount of carbon dioxide adsorption is significantly increased in Test Example 9-2 compared to Test Example 9-1, and in Test Example 10-2 compared to Test Example 10-1. It is therefore believed that the porosity of the carbon raw material is improved by removing the low boiling point components of 250°C or less from the carbon raw material.

[0065] Extracts of biomass such as coniferous and broad-leaved trees have a high oxygen content, such as the extracts of coniferous trees in Test Examples 9 and 10, and even if the poor solvent method is simply applied, it may not be possible to obtain porous carbon with a large pore volume. However, even with such carbon raw materials, the porosity of the porous carbon obtained by the production method can be easily improved by removing the low boiling point components. Therefore, removing the low boiling point components from the carbon raw material is considered to be a significant modification method. [Industrial Applicability]

[0066] As described above, the method for producing porous carbon of the present invention can stably produce porous carbon having excellent gas adsorption properties, and the obtained porous carbon can be suitably used as a molecular sieve, a gas storage material, etc.

Claims

1. Dissolving the carbon raw material in a good solvent; mixing the solution obtained in the dissolving step with a poor solvent for the carbon raw material; A step of separating the precipitated solid matter from the mixed liquid obtained in the mixing step; Equipped with A method for producing porous carbon, wherein the yield of the carbon raw material is 35 mass% or more when heated up to 1000°C in an inert atmosphere.

2. The method for producing porous carbon according to claim 1 , wherein the yield is 70 mass % or less.

3. 3. The method for producing porous carbon according to claim 1, further comprising the step of removing low-boiling point components from the carbon raw material before the dissolving step.

4. 3. The method for producing porous carbon according to claim 1, wherein the content of components having a boiling point of 250° C. or less in the carbon raw material is 1 mass % or less.

5. The method for producing porous carbon according to claim 1 or 2, further comprising a step of solid-phase carbonizing the solid content separated in the separation step.

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