Porous carbon for acidic gas solid absorbing material carrier, acidic gas solid absorbing material, method for separating and recovering acidic gas, and acidic gas separation and recovery system

Abstract

The present invention pertains to a porous carbon for an acidic gas solid absorbing material carrier, wherein: the volume of pores having a pore diameter of 2-200 nm, as calculated by a BJH method from a nitrogen adsorption isotherm, is at least 0.7 cm3 / g; and the ratio of the volume of pores having a pore diameter of at most 2 nm, as calculated by a QS-DFT method from the nitrogen adsorption isotherm, to the sum of the volume of pores having a pore diameter of 2-200 nm, as calculated by the BJH method, and the volume of pores having a pore diameter of at most 2 nm, as calculated by the QS-DFT method, is at most 45%.

Description

Porous carbon for use as a carrier for a solid acid gas absorbent, a solid acid gas absorbent, a method for separating and recovering acid gases, and an acid gas separation and recovery system

[0001] The present invention relates to porous carbon for use as a carrier for a solid acid gas absorbent, a solid acid gas absorbent comprising porous carbon and an acid gas absorbent impregnated on the porous carbon, a method for separating and recovering acid gases using the solid absorbent, and an acid gas separation and recovery system comprising the solid absorbent.

[0002] Carbon dioxide emitted from industries, automobiles, and households is considered a cause of global warming. Furthermore, sulfur oxides (SOx) and nitrogen oxides (NOx), which are generated by the combustion of fossil fuels such as coal and oil or by nitrogen oxidation reactions in automobile engines, are considered to be causes of environmental acidification. Efforts to reduce these acidic gases are being undertaken worldwide. One such effort is the development of carbon dioxide separation and capture technologies. Sources of large amounts of carbon dioxide include thermal power plants, steel mills, cement plants, and oil refineries. At least some of these facilities capture carbon dioxide using separation and capture techniques such as physical absorption, chemical absorption, solid absorption, and membrane separation. The chemical absorption method primarily uses solid absorbents. For example, a carbon dioxide adsorbent, which is made by incorporating an amine compound, which is highly reactive with carbon dioxide gas, into a porous material, is known (Patent Document 1). The solid adsorbent, which can efficiently recover acidic gases and increase the amount of recovered acidic gases, contains an inorganic porous material and an amine compound, and the inorganic porous material has a pore volume of 1.2 cm3. ３ / g or more 3.5cm ３ / g or less, and the peak pore diameter, as determined by a nitrogen adsorption method, is 20 nm or more and 100 nm or less (Patent Document 2). Examples of acidic gas separation and recovery systems using solid absorbents include fixed-bed acidic gas separation and recovery systems in which the gas to be treated is alternately introduced into two towers packed with solid absorbents, and the acidic gas is continuously recovered by alternately absorbing the acidic gas and regenerating the solid absorbent; and moving-bed acidic gas separation and recovery systems in which the solid absorbent moves through the system by a conveyor, honeycomb rotor / container, or the like, absorbs acidic gas from the gas to be treated in the absorption zone, releases the absorbed acidic gas in the regeneration zone, and recovers the released acidic gas. In acidic gas separation and recovery systems such as those described above, reducing the energy and cost required for separation and recovery is important. To increase the amount of processing per hour, it is necessary to shorten the time required for one cycle in the system and improve the efficiency of separation and recovery of acidic gases. For example, in an existing moving-bed carbon dioxide separation and capture system that includes a honeycomb rotor, the rotation time of the honeycomb rotor and the time it takes to pass through the absorption zone and the regeneration (desorption) zone vary depending on the diameter and volume of the honeycomb rotor. For example, in an existing system, the honeycomb rotor makes one rotation in about 3 to 5 minutes, and the rotating honeycomb rotor passes through the absorption zone in about 30 to 180 seconds.

[0003] Japanese Patent Application Laid-Open No. 4-200742 International Publication No. 2022 / 102683

[0004] According to the studies of the present inventors, there is a need for a highly efficient solid carbon dioxide absorbent that has high carbon dioxide adsorption and desorption rates in a short time (for example, 30 seconds to several minutes, preferably 30 seconds to 180 seconds) and high carbon dioxide adsorption and desorption amounts. An object of the present invention is to provide a porous carbon for use as a support for a solid acidic gas absorbent that has an excellent acidic gas adsorption and desorption rate in a short time and a high acidic gas adsorption and desorption amount when used as a support for a solid acidic gas absorbent in the separation and recovery of acidic gases such as carbon dioxide.

[0005] The present inventors have conducted extensive research into porous carbon in order to solve the above-mentioned problems, and as a result have completed the present invention. That is, the present invention encompasses the following preferred embodiments: [1] The pore volume of porous carbon having a pore diameter of 2 nm or more and 200 nm or less calculated from a nitrogen adsorption isotherm by the BJH method is 0.7 cm ３ / g or more, and the ratio of the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method from the nitrogen adsorption isotherm is 45% or less. [2] In the measurement of the nitrogen adsorption isotherm, the pressure change of nitrogen until adsorption equilibrium is reached at each predetermined relative pressure is converted into a mass transfer coefficient using the LDF approximation, and the mass transfer coefficient is calculated by the LDF approximation to obtain a mass transfer coefficient when the relative pressure is 1.0 x 10 －４ Above 1.0 x 10 －３ [3] The porous carbon according to [1], wherein the gradient of an approximate line obtained by linearly approximating the relationship between the relative pressure and the mass transfer coefficient in the following is 0.95 or more. ３ [4] The porous carbon according to any one of [1] to [3], wherein the acidic gas is carbon dioxide. [5] A solid acidic gas absorbent comprising the porous carbon according to any one of [1] to [4] and an acidic gas absorbent, wherein the acidic gas absorbent is impregnated into the porous carbon. [6] The solid acidic gas absorbent according to [5], wherein the acidic gas absorbent is an amine compound. [7] The pore volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method from a nitrogen adsorption isotherm is 0.7 cm ３The solid acidic gas absorbent according to [5] or [6], wherein the ratio of the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method from a nitrogen adsorption isotherm is 40% or less.[8] A method for separating and recovering acidic gases, comprising an absorption step of contacting a gas to be treated with the solid acidic gas absorbent according to any one of [5] to [7] to absorb the acidic gas, and a desorption step of desorbing the acidic gases absorbed in the absorption step from the solid acidic gas absorbent, wherein the desorption step comprises at least one step selected from the group consisting of (A) applying a reduced pressure to the solid acidic gas absorbent, (B) contacting an inert gas not containing acidic gas, and (C) heating. [9] A moving bed acidic gas separation and recovery system, comprising a moving bed containing the solid acidic gas absorbent according to any one of [5] to [7].

[10] The moving bed acidic gas separation and recovery system according to [9], comprising a rotating honeycomb rotor as a means for moving the solid acidic gas absorbent, and the solid acidic gas absorbent is supported on the rotating honeycomb rotor.

[0006] According to the present invention, it is possible to provide a porous carbon for use as a support for a solid acidic gas absorbent, which, when used as a support for a solid acidic gas absorbent in the separation and recovery of acidic gases such as carbon dioxide, has an excellent acidic gas adsorption / desorption rate in a short period of time and a high acidic gas adsorption / desorption amount.

[0007] 1 is a graph showing the relationship between relative pressure and mass transfer coefficient for the porous carbon of Example 1. 2 is a graph showing the amount of carbon dioxide adsorption per 1 g of each solid absorbent for solid absorbents 1-1 to 1-5 and 4-1 to 4-5. 3 is a graph showing the carbon dioxide adsorption rate per 1 g of each solid absorbent for solid absorbents 1-1 to 1-5 and 4-1 to 4-5.

[0008] Hereinafter, embodiments of the present invention will be described in detail. Note that the following description is merely illustrative of embodiments of the present invention, and is not intended to limit the present invention to the following embodiments.

[0009] [Porous Carbon] The porous carbon for use as a carrier for a solid acidic gas absorbent of the present invention has a pore volume of 0.7 cm3 of pores with a pore diameter of 2 nm or more and 200 nm or less, calculated from a nitrogen adsorption isotherm by the BJH method. ３ / g or more, and has a characteristic pore structure in which the ratio of the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method from a nitrogen adsorption isotherm is 45% or less.

[0010] <Pore volume of pores with a diameter of 2 nm or more and 200 nm or less> In porous carbon, the lower limit of the volume of pores with a diameter of 2 nm or more and 200 nm or less (hereinafter sometimes referred to as "pore volume of 2 nm or more and 200 nm or less") calculated from a nitrogen adsorption isotherm by the BJH method is 0.7 cm ３ / g, and the upper limit is not particularly limited, but is usually 4.00 cm ３ The pore volume of 2 nm or more and 200 nm or less is preferably 0.80 to 4.00 cm ３ / g, more preferably 0.90 to 3.90 cm ３ / g, more preferably 1.00 to 3.80 cm ３ / g, and even more preferably 1.30 to 3.70 cm ３ / g, particularly preferably 1.60 to 3.60 cm ３ / g, more particularly preferably 1.70 to 3.50 cm ３ / g, very preferably 1.80 to 3.40 cm ３ / g, more highly preferably 1.90 to 3.30 cm ３ / g. Pores of 2 nm or more and 200 nm or less are thought to be involved in the impregnation of the acidic gas absorbent (for example, an amine compound when the acidic gas is carbon dioxide) to the porous carbon, and in the adsorption and desorption of the acidic gas of the solid acidic gas absorbent. If the pore volume of 2 nm or more and 200 nm or less is equal to or greater than the lower limit, when the porous carbon is used as a carrier for the solid acidic gas absorbent, a sufficient amount of the acidic gas absorbent can be impregnated to the porous carbon, and further, the porous carbon tends to have a pore structure that can maintain pores that allow the acidic gas to move smoothly even after the acidic gas absorbent is impregnated, so that the solid acidic gas absorbent can have an excellent acidic gas adsorption / desorption rate and a high acidic gas adsorption / desorption amount in a short time (for example, 30 seconds to several minutes, preferably 30 seconds to 180 seconds). When the pore volume of 2 nm or more and 200 nm or less is 0.7 cm ３ When the pore volume of the porous carbon having a diameter of 2 nm or more and 200 nm or less is equal to or less than the upper limit, the porous carbon can have sufficient strength to maintain its structure.

[0011] The pore volume of 2 nm or more and 200 nm or less can be adjusted to be equal to or more than the lower limit and equal to or less than the upper limit, or within the above range, by, for example, appropriately adjusting the types and / or ratios of the carbon source and pore source, the type of metal organic acid, the temperature and / or time of the heat treatment step (phase separation step and / or carbonization step) in the method for producing porous carbon described below. The pore volume of 2 nm or more and 200 nm or less can be calculated by analyzing the nitrogen adsorption isotherm of the porous carbon by the BJH method, which is known in the art.

[0012] <Volume of pores of 2 nm or less by nitrogen adsorption method> In a preferred embodiment, the upper limit of the volume of pores of pores of 2 nm or less in diameter (hereinafter sometimes referred to as "volume of pores of 2 nm or less" or "micropore volume") calculated by the QS-DFT method from the nitrogen adsorption isotherm of the porous carbon is preferably 0.35 cm ３ / g, and the lower limit is not particularly limited, but is preferably 0.01 cm ３ The pore volume of pores with a diameter of 2 nm or less is preferably 0.01 to 0.35 cm ３ / g, more preferably 0.01 to 0.30 cm ３ / g, more preferably 0.01 to 0.20 cm ３ / g, particularly preferably 0.01 to 0.15 cm ３ / g. When the micropore volume is equal to or less than the upper limit, the volume of pores with a pore diameter of 2 to 200 nm tends to be high, and therefore, the solid acidic gas absorbent can have an excellent acidic gas adsorption / desorption rate in a short time and a high acidic gas adsorption / desorption amount. The pore volume of pores with a pore diameter of 2 nm or less can be adjusted to be equal to or more than the lower limit and equal to or less than the upper limit, or within the range, by appropriately adjusting, for example, the type and / or ratio of the carbon source and pore source; the type of metal organic acid; the temperature and / or time of the heat treatment step (phase separation step and / or carbonization step) in the method for producing porous carbon described below. The pore volume of pores with a pore diameter of 2 nm or less can be calculated by analyzing the nitrogen adsorption isotherm of the porous carbon using the QS-DFT method, which is known in the art.

[0013] <Ratio of the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method> The ratio of the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method (sometimes referred to as the micropore ratio) is calculated using the following formula. The upper limit of the micropore ratio is 45%, and the lower limit is not particularly limited, but is typically 0%. The micropore ratio is preferably 0 to 45%, more preferably 0 to 40%, even more preferably 0 to 30%, still more preferably 0 to 25%, particularly preferably 0 to 20%, even more particularly preferably 0 to 15%, extremely preferably 0 to 10%, and most extremely preferably 0 to 5%. When an acidic gas absorbent is impregnated into porous carbon, pores of 2 nm or less are blocked or constricted by the acidic gas absorbent, and are therefore not useful for the desired adsorption and desorption of acidic gases. When the micropore ratio is below the upper limit, the volume of pores of 2 nm or less tends to be small. Therefore, a sufficient amount of acidic gas absorbent can be impregnated into the porous carbon, and pores through which acidic gases can smoothly move can be maintained even after the acidic gas absorbent is impregnated. Therefore, the solid acidic gas absorbent can have an excellent acidic gas adsorption / desorption rate in a short period of time and a high acidic gas adsorption / desorption amount.

[0014] <Relationship between Mass Transfer Coefficient and Relative Pressure, and Mass Transfer Coefficient> The mass transfer coefficient of porous carbon is an index representing the speed at which acid gases move through the pores of a solid acid gas absorbent produced using porous carbon. The greater the change in mass transfer coefficient with respect to a change in relative pressure, the more smoothly acid gases can move from mesopores to micropores, and vice versa. Furthermore, the greater the mass transfer coefficient, the faster the acid gas moves through the pores of the solid acid gas absorbent. Therefore, by examining the change in mass transfer coefficient with respect to a change in relative pressure and the value of the mass transfer coefficient, it is possible to evaluate the pore characteristics of porous carbon, which are useful for the acid gas adsorption / desorption properties of a solid acid gas absorbent and the acid gas adsorption / desorption properties of a solid acid gas absorbent. Here, according to IUPAC, micropores refer to pores with a diameter of 2 nm or less, and mesopores refer to pores with a diameter of 2 to 50 nm. The relationship between relative pressure and mass transfer coefficient, and the mass transfer coefficient, can be investigated by creating an adsorption isotherm by adsorbing nitrogen gas onto porous carbon at -196°C and analyzing this adsorption isotherm. Specifically, as described in the Examples below, for example, a nitrogen adsorption isotherm for porous carbon is created, and the change in nitrogen pressure until adsorption equilibrium is reached at each predetermined relative pressure is converted into a mass transfer coefficient using the LDF approximation. Next, the relationship between relative pressure and mass transfer coefficient can be represented by creating a graph with relative pressure on the x-axis and mass transfer coefficient on the y-axis.

[0015] In this graph, the relative pressure is 1.0 x 10 －４ Above 1.0 x 10 －３ The gradient of the approximate line drawn in the following range (hereinafter, this gradient may be referred to as gradient (a)) is preferably 0.95 or more. －４ Above 1.0 x 10 －３The reasons for the settings are explained below. The porous carbon of the present invention is used as a carrier for a solid absorbent for absorbing acidic gases. The solid absorbent comprises porous carbon and an acidic gas absorbent impregnated on the porous carbon. At least a portion of the pores of the porous carbon is blocked or narrowed by the impregnated acidic gas absorbent. In this specification, pores with a diameter of about 2 to 200 nm, at least a portion of which is impregnated with the acidic gas absorbent, are assumed to serve as diffusion paths for acidic gases adsorbed on the acidic gas absorbent. If the relative pressure is too low, i.e., if the relative pressure is less than 1.0 × 10 －４ On the other hand, if the relative pressure is too high, that is, if the relative pressure is less than 1.0 × 10, the diffusion behavior in pores smaller than those that effectively function as migration paths for acidic gases is considered to be reflected in the mass transfer coefficient. －３ When the relative pressure is 1.0×10, the diffusion behavior in the pores larger than the pores that effectively function as the transfer path of such acid gases is considered to be reflected in the mass transfer coefficient. －４ Above 1.0 x 10 －３ By setting the following, it is possible to evaluate the region in which the adsorption / desorption behavior of acidic gases assumed in this specification is reflected in the mass transfer coefficient, and by examining the slope of the approximation line within this range, it is possible to evaluate the acidic gas adsorption / desorption characteristics of the solid acidic gas absorbent and the pore characteristics of the porous carbon, which are useful for the acidic gas adsorption / desorption characteristics of the solid acidic gas absorbent.

[0016] A more specific method for determining the slope (a) will be described using the graph shown in Figure 1, which shows the relationship between the relative pressure and the mass transfer coefficient for the porous carbon of Example 1 described later. First, the slope (a) is calculated for a relative pressure of 1.0 x 10 －４ Above 1.0 x 10 －３ An approximate line is drawn in the following range (in FIG. 1, this range is indicated by a dashed line and an arrow): Next, the slope (a) of this approximate line is found.

[0017] The slope (a) is preferably 0.95 or greater and, although not limited thereto, is typically 10 or less. The slope (a) is preferably 0.95 to 10, more preferably 1 to 10, even more preferably 1.5 to 10, even more preferably 2 to 10, particularly preferably 3 to 10, even more particularly preferably 4 to 10, extremely preferably 5 to 10, and most extremely preferably 6 to 10. When the slope (a) is equal to or greater than the aforementioned lower limit, when the porous carbon is used as a carrier for a solid acidic gas absorbent, the porous carbon tends to have a suitable pore structure that allows a sufficient amount of acidic gas absorbent to be impregnated therewith and that can maintain pores that allow smooth movement of acidic gases even after the acidic gas absorbent is impregnated therewith, thereby enabling the solid acidic gas absorbent to have an excellent acidic gas adsorption / desorption rate in a short period of time and a high acidic gas adsorption / desorption amount. Furthermore, when the slope (a) is equal to or greater than the aforementioned lower limit, the porous carbon tends to have many mesopores and pores ranging from 2 nm to 200 nm.

[0018] The relative pressure of the approximate straight line in the above range is 1.0 x 10 －３ The mass transfer coefficient (hereinafter, this value may be referred to as the mass transfer coefficient (b)) is preferably 2.0×10 －４ seconds ―１ or more, and is usually, but not limited to, 1.0 × 10 －２ seconds －１ The mass transfer coefficient (b) is more preferably 2.0 x 10 －４ ~1.0 x 10 －２ seconds －１ , 5.0 × 10 ―４ ~9.0 x 10 －３ seconds －１ , 1.0×10 －３ ~8.0 x 10 －３ seconds －１ , 2.0 × 10 －３ ~7.0 x 10 －３ seconds －１ , 2.5 × 10 －３ ~6.0 x 10 －３ seconds －１When the mass transfer coefficient (b) is equal to or greater than the lower limit, the porous carbon tends to have a pore structure that is more suitable for the transfer of acidic gases when a solid acidic gas absorbent is produced using the porous carbon, and therefore such a solid acidic gas absorbent can exhibit an excellent acidic gas adsorption / desorption rate in a short time and a high amount of acidic gas adsorption / desorption. Explained using the graph shown in FIG. 1, the mass transfer coefficient (b) is －３ (the right end of the dashed line or arrow on the right) is the mass transfer coefficient.

[0019] The "suitable pore structure" described above is considered to be a pore structure having many pores that function effectively as migration paths for acidic gases, the openings of such pores having suitable dimensions for the ingress and egress of acidic gases, and a high proportion of pores that are open from one end opening to the other end opening (pores that have an opening at one end and are not blocked at the other end). Furthermore, if the gas migration path is relatively short or there are few structures (e.g., bottlenecks) that hinder the migration of acidic gases at the communication part, the migration rate of acidic gases in the pores of the solid acidic gas absorbent is considered to be faster, and the amount of acidic gas adsorption / desorption is considered to be greater. In a preferred embodiment of the present invention, all pores are considered to be open from the opening at one end to the opening at the other end. Furthermore, the slope (a) is considered to correspond to the length of the path along which acidic gases move through the solid acidic gas absorbent for adsorption or desorption, and the greater the slope (a), the shorter the path length. The mass transfer coefficient (b) is thought to correspond to the amount of structure that hinders the movement of acidic gases in the communicating portion, and it is thought that the larger the mass transfer coefficient (b), the less structure that hinders the movement of acidic gases.

[0020] Porous carbon having a gradient (a) equal to or greater than the lower limit can be produced, for example, by heat-treating a mixture in which a carbon source and a pore source are mixed in a highly compatible state, followed by carbonization to fix the phase-separated structure, and then removing the pore source from the resulting carbide. For example, in the method for producing porous carbon described below, the gradient (a) can be adjusted to equal to or greater than the lower limit or within the range by appropriately adjusting the temperature and time during which a mixture of a carbon source and a calcium compound serving as a pore source is heat-treated, or by changing the type of carbon source and appropriately adjusting the temperature and time during which the mixture is heat-treated. Furthermore, the mass transfer coefficient (b) can also be adjusted to equal to or greater than the lower limit or within the range by appropriately adjusting similar conditions.

[0021] <Bulk density> The bulk density of porous carbon indicates the degree of development of the pore structure. When the pore volumes of pores with diameters of 2 nm to 200 nm are the same, the lower the bulk density, the larger the volume of pores with diameters exceeding 200 nm. Pores with diameters of 2 nm to 200 nm contribute to the movement of acidic gases when a solid acidic gas absorbent is produced using the porous carbon and to the impregnation of the acidic gas absorbent to the porous carbon, while pores with diameters exceeding 200 nm are thought to serve as entrances or migration paths for the acidic gas absorbent and the acidic gases when a solid acidic gas absorbent is produced using the porous carbon to smoothly move into the pores with diameters of 2 nm to 200 nm. Therefore, in addition to the volume of pores with diameters of 2 nm to 200 nm, it is preferable that the volume of pores with diameters of 200 nm or more is large, i.e., the bulk density is small.

[0022] In a preferred embodiment, the upper limit of the bulk density of the porous carbon is preferably 0.17 g / cm ３ The lower limit is not particularly limited, but is usually 0.001 g / cm ３ The bulk density of the porous carbon is preferably 0.001 to 0.17 g / cm ３ less than 0.005 to 0.15 g / cm ３ , more preferably 0.006 to 0.12 g / cm ３ , particularly preferably 0.01 to 0.10 g / cm ３When the porous carbon has a bulk density less than or equal to the upper limit, when the porous carbon is used as a carrier for a solid acidic gas absorbent, a sufficient amount of the acidic gas absorbent can be impregnated onto the porous carbon. Furthermore, the porous carbon tends to have a pore structure that allows the acidic gas to smoothly move through the pores even after the acidic gas absorbent is impregnated. Therefore, the solid acidic gas absorbent can have an excellent acidic gas adsorption / desorption rate in a short time and a high acidic gas adsorption / desorption amount. When the porous carbon has a bulk density equal to or greater than the lower limit, scattering can be suppressed and handling can be improved when the porous carbon is used as a carrier for a solid acidic gas absorbent. Furthermore, the carbon skeleton has a certain level of strength and can maintain the pore structure. The bulk density can be adjusted to be less than the upper limit or within the above range, for example, by appropriately adjusting the type and / or ratio of the carbon source and the pore source; the type of metal organic acid; the temperature and / or time of the heat treatment step (phase separation step and / or carbonization step) in the method for producing porous carbon described below. The bulk density can be measured by the method described in the Examples described below.

[0023] <Specific surface area calculated by BET method> In a preferred embodiment, the specific surface area of ​​the porous carbon calculated by the BET method from the nitrogen adsorption isotherm is preferably 300 to 1500 m ２ / g, more preferably 400 to 1400 m ２ / g, more preferably 450 to 1300 m ２ / g, particularly preferably 500 to 1200 m ２ / g. When the specific surface area is within this range, when the porous carbon is used as a carrier for a solid acidic gas absorbent, a sufficient amount of the acidic gas absorbent can be impregnated onto the porous carbon, and the porous carbon tends to have a pore structure that can maintain pores that allow smooth movement of acidic gases even after the acidic gas absorbent is impregnated. This allows the solid acidic gas absorbent to have an excellent acidic gas adsorption / desorption rate in a short period of time and a high acidic gas adsorption / desorption amount. The specific surface area can be adjusted to within this range, for example, by appropriately adjusting the type and / or ratio of the carbon source and the pore source; the type of metal organic acid; the temperature and / or time of the heat treatment step (phase separation step and / or carbonization step) in the method for producing porous carbon described below. The specific surface area can be calculated by measuring the adsorption isotherm of the porous carbon, analyzing the adsorption isotherm using the BET equation by a multipoint method, and approximating the obtained curve in the relative pressure range of 0.05 to 0.1.

[0024] <Calcium Content> In a preferred embodiment, the calcium content of the porous carbon is preferably 20 to 2000 ppm, more preferably 50 to 1500 ppm, and even more preferably 100 to 1000 ppm. When the calcium content is within this range, excessive increases in the mass of the porous carbon tend to be suppressed, and productivity also tends to be excellent. The calcium content can be adjusted to within this range, for example, by appropriately adjusting the conditions of the step of removing the pore source or oxides derived therefrom (e.g., the type and / or concentration of the acid used in acid washing, the time and / or temperature of acid washing, etc.) in the method for producing porous carbon described below.

[0025] <Sulfur Content and Silicon Content> In a preferred embodiment, the sulfur and silicon contents in the porous carbon are each preferably 1000 ppm or less, and although the lower limit thereof is not particularly limited, is 0 ppm. The sulfur content in the porous carbon is preferably 0 to 1000 ppm, more preferably 0 to 900 ppm, and even more preferably 0 to 800 ppm. Furthermore, in a preferred embodiment, the silicon content in the porous carbon is preferably 0 to 1000 ppm, more preferably 0 to 900 ppm, and even more preferably 0 to 800 ppm. When the sulfur and silicon contents are not more than the above upper limit values ​​or within the above ranges, excessive increases in the mass of the porous carbon tend to be suppressed, and productivity also tends to be excellent. The sulfur and silicon contents can be adjusted to be equal to or less than the upper limit or within the above ranges, for example, by appropriately selecting the type of carbon source in the method for producing porous carbon described below, and / or by appropriately adjusting the conditions of the step of removing the pore source or oxides derived therefrom (e.g., the type and / or concentration of the acid used in acid washing, the time and / or temperature of acid washing, etc.). The calcium, sulfur, and silicon contents can be measured by fluorescent X-ray analysis.

[0026] [Method for producing porous carbon] The porous carbon of the present invention can be produced by a method comprising, for example, the steps of: (1) obtaining a mixture containing a carbon source and a calcium compound as a pore source; (2) heat-treating the mixture in an inert gas atmosphere to cause phase separation into the carbon source and the calcium compound; (3) heat-treating the phase-separated mixture in an inert gas atmosphere to obtain a carbide; (4) removing the calcium compound from the carbide to obtain porous carbon; and (5) optionally, pulverizing the porous carbon.

[0027] <Step (1)> The carbon source is not particularly limited. From the viewpoint of increasing compatibility with the calcium compound that serves as the pore source, the carbon source is preferably a sugar. Examples of sugars include monosaccharides such as glucose, galactose, mannose, fructose, ribose, and glucosamine; disaccharides such as sucrose, trehalose, maltose, cellobiose, maltitol, lactobionic acid, and lactosamine; and polysaccharides such as starch, cellulose, glycogen, pectin, curdlan, and guar gum. These sugars can be used alone or in combination of two or more. Among these sugars, glucose and starch are preferred from the viewpoints of ease of producing porous carbon having a suitable pore structure and ease of mass procurement.

[0028] The starch is not particularly limited, and starches derived from, for example, corn, cassava, potato, sweet potato, tapioca, beans, wheat, rice, etc. can be used. The amylose content of the starch is preferably 50% by mass or less, more preferably 30% by mass or less, based on the mass of the starch. The lower the amylose content of the starch, the lower the gelatinization temperature tends to be. Therefore, starch having an amylose content below the upper limit is preferred because it is more likely to gelatinize at low temperatures and to have increased compatibility with calcium compounds that serve as pore-forming materials. The amylose content can be determined, for example, by iodine colorimetry. The starch may also be modified starch. Examples of modified starches include etherified starch, esterified starch, cationized starch, and cross-linked starch. One type of starch may be used alone, or two or more types may be used in combination. When two or more starches are used in combination, the amylose content is the average amylose content of the combined starches.

[0029] The pore source is not particularly limited. From the viewpoint of easily increasing compatibility with the carbon source, the pore source is preferably a calcium compound. The calcium compound is not particularly limited, and examples thereof include calcium chloride, calcium hydroxide, calcium oxide, calcium carbonate, calcium acetate, calcium fluoride, calcium bromide, calcium iodide, calcium carbide, calcium bicarbonate, calcium nitrate, calcium sulfate, calcium silicate, calcium phosphate, calcium pyrophosphate, calcium gluconate, and calcium lactate. Among these calcium compounds, from the viewpoint of easily producing porous carbon exhibiting excellent gas diffusibility, calcium compounds having a melting point of 300°C or less (when the mixture contains water and / or a polyhydric alcohol and / or a carboxylic acid, the melting point of a eutectic compound of the calcium compound, the carbon source, and water and / or a polyhydric alcohol and / or a carboxylic acid is 300°C or less) are preferred, and at least one selected from the group consisting of calcium chloride hydrate, calcium hydroxide, calcium oxide, calcium carbonate, and calcium acetate is more preferred. Calcium chloride hydrate exists as a dihydrate, a tetrahydrate, and a hexahydrate, and any of the hydrates may be used, but the dihydrate is preferred because of its good reactivity with sugars.

[0030] The mixture containing a carbon source and a calcium compound may further contain at least one selected from the group consisting of water, a polyhydric alcohol, and a carboxylic acid. It is believed that the presence of water and / or a polyhydric alcohol and / or a carboxylic acid in the mixture allows the carbon source and the calcium compound to dissolve in each other via the water and / or the polyhydric alcohol and / or the carboxylic acid, forming a eutectic compound. This allows a calcium compound that has a melting point of 300°C or higher alone to have a melting point of 300°C or lower as the melting point of the eutectic compound. Therefore, in this specification, "the melting point of the calcium compound is 300°C or lower" also encompasses "the melting point of the eutectic compound of water and / or a polyhydric alcohol and / or a carboxylic acid with the carbon source and the calcium compound is 300°C or lower." Water is preferred due to its availability. Usable polyhydric alcohols include, for example, glycerin, ethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol. Among these polyhydric alcohols, glycerin and ethylene glycol are preferred due to their ease of dissolving calcium compounds and their availability in large quantities. Examples of carboxylic acids that can be used include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, lactic acid, malic acid, citric acid, benzoic acid, phthalic acid, salicylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid. Among these carboxylic acids, formic acid and acetic acid are preferred because they easily dissolve calcium compounds and are readily available in large quantities. When a mixture of two or more of water, one or more polyhydric alcohols, and one or more carboxylic acids is used, the ratio of the water, polyhydric alcohols, and two or more carboxylic acids can be appropriately changed depending on the desired properties of the porous carbon.

[0031] The method for mixing the carbon source and calcium compound, and optionally water, polyhydric alcohol and / or carboxylic acid, is not particularly limited, and they can be mixed by any mixing method.

[0032] The amount of the calcium compound mixed with the carbon source is preferably 80 to 500 parts by mass, more preferably 130 to 400 parts by mass, and even more preferably 180 to 300 parts by mass, relative to 100 parts by mass of the carbon source. When the amount of the calcium compound is within the above range, the relationship between the mass transfer coefficient and the relative pressure, and the pore volume of the resulting porous carbon can be favorable.

[0033] When the mixture containing a carbon source and a calcium compound further contains water and / or a polyhydric alcohol and / or a carboxylic acid, the amount of water and / or a polyhydric alcohol and / or a carboxylic acid (when two or more of water, one or more polyhydric alcohols, and one or more carboxylic acids are used, the total amount) is preferably 50 to 500 parts by mass, more preferably 100 to 400 parts by mass, and even more preferably 150 to 300 parts by mass per 100 parts by mass of the carbon source. However, when the mixture containing a carbon source and a calcium compound contains water but not a polyhydric alcohol or a carboxylic acid, the amount of water is preferably 10 to 500 parts by mass, more preferably 20 to 400 parts by mass, and even more preferably 50 to 300 parts by mass per 100 parts by mass of the carbon source. When the amount of water and / or a polyhydric alcohol and / or a carboxylic acid is within the above range, a eutectic compound is likely to form, thereby enabling the resulting porous carbon to have a favorable relationship between the mass transfer coefficient and the relative pressure, and a favorable pore volume.

[0034] <Step (2)> In step (2), the mixture obtained in step (1) is heat-treated in an inert gas atmosphere to separate the carbon source and the calcium compound into phases. Examples of inert gases include nitrogen, argon, and mixtures thereof. The lower the concentration of the oxidizing gas in the gas used, the better. The concentration of the oxidizing gas, particularly oxygen, is typically 1% by volume or less, more preferably 0.1% by volume or less, based on the volume of the gas used. When the concentration of the oxidizing gas is below the upper limit, oxidation of the mixture is suppressed, making it easier to obtain a structure with the desired characteristics. Furthermore, oxidative decomposition of the resulting structure can be suppressed. The supply (flow) rate of the inert gas is typically 200 to 7,000 mL / min, preferably 500 to 6,000 mL / min, and more preferably 1,000 to 5,000 mL / min per gram of the mixture.

[0035] The heat treatment temperature is preferably 150 to 500°C, more preferably 200 to less than 500°C, even more preferably 240 to 470°C, particularly preferably 250 to 450°C, even more particularly preferably greater than 300°C to 420°C, and even more particularly preferably greater than 300°C to 400°C. The present inventors have found that the pore structure of the porous carbon of the present invention can be obtained by heat treating the mixture obtained in step (1) in an inert gas atmosphere, preferably at a temperature within the above range. The reason for this is not clear, but the following non-limiting mechanism of action is thought to be involved.

[0036] The heat treatment causes phase separation of the carbon source and the calcium compound, which has been compatible with the carbon source through hydrogen bonding, in the mixture, triggered by the elimination of hydration water from the mixture or the dehydration reaction of the carbon source. Furthermore, as the dehydration reaction of the carbon source progresses, the carbon source hardens, and the structure in which the carbon source and the calcium compound are phase-separated is believed to be fixed. At this time, at least a portion of the phase-separated calcium compounds (preferably 50% by mass or more, more preferably almost all or all of the phase-separated calcium compounds) are continuously connected in a three-dimensional manner. In the subsequent carbonization step, the carbon source is aromatized (carbonized) to make it insoluble in hot water or hot acid. In the subsequent calcium compound removal step, the calcium compounds are removed from the carbonized product (preferably by washing with acid). Because the areas where the calcium compounds have been removed become pores, the phase separation of the calcium compounds by the heat treatment is believed to result in the porous carbon structure of the present invention.

[0037] The temperature rise rate during the heat treatment step is preferably 2°C / min or more, and although there is no particular upper limit, it is preferably 200°C / min or less from the viewpoint of easily achieving uniform heat treatment. The temperature rise rate during the heat treatment step is preferably 2 to 200°C / min, more preferably 5 to 200°C / min, and even more preferably 10 to 200°C / min. When the temperature rise rate is equal to or greater than the lower limit, it is easy to obtain the desired pore volume and / or the desired mass transfer coefficient.

[0038] The heat treatment time is appropriately selected depending on the heat treatment temperature, the amount of inert gas supplied, etc. For example, it is 0.1 to 24 hours, preferably 0.2 to 24 hours, more preferably 0.3 to 12 hours, and even more preferably 0.5 to 8 hours. When the heat treatment time is equal to or greater than the lower limit, phase separation tends to proceed sufficiently. When the heat treatment time is equal to or less than the upper limit, it is an appropriate time from the viewpoint of economy, and is therefore preferred.

[0039] The heat treatment may be performed using various furnaces such as rotary kilns, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and moving bed furnaces, as well as various dryers such as spray dryers, moving dryers, agitator dryers, roll dryers, and thin film evaporators. A continuous furnace or dryer may be used, which continuously introduces the material to be heat-treated and removes the material after heat treatment, or a batch furnace or dryer may be used, which does so discontinuously. The heating means may be any means capable of heating to a predetermined temperature, such as electric heating, gas combustion heating, microwave heating, high-frequency induction heating, or electrical heating. These heating means may be used alone or in combination.

[0040] <Step (3)> In step (3), the mixture phase-separated in step (2) is heat-treated in an inert gas atmosphere to carbonize it. The heat treatment temperature is preferably 500 to 1300°C, more preferably greater than 550°C to 1200°C, even more preferably 600 to 1100°C, and particularly preferably 650 to 1000°C. When the heat treatment temperature is within this range, the resulting porous carbon tends to have an appropriate pore volume of 2 nm to 200 nm. When the porous carbon is used as a support for a solid acidic gas absorbent, a sufficient amount of the acidic gas absorbent can be impregnated into the porous carbon. Furthermore, the porous carbon can have a pore structure that maintains pores that allow smooth movement of acidic gases even after the acidic gas absorbent is impregnated. Furthermore, this facilitates the removal of calcium compounds from the charcoal in the subsequent step of removing calcium compounds. The phase-separated mixture may be heat-treated in multiple stages. For example, the mixture may be heat-treated at 500 to 900°C, followed by heat treatment at 900 to 1300°C. In the solid acidic gas absorbent produced using porous carbon, it is preferable not to carry out the heat treatment in multiple stages, from the viewpoint of easily obtaining porous carbon that provides an excellent acidic gas adsorption rate and acidic gas adsorption amount in a short period of time. However, carrying out the heat treatment in multiple stages is not excluded.

[0041] The temperature rise rate during the heat treatment step is preferably 2°C / min or more, and although there is no particular upper limit, it is preferably 200°C / min or less from the viewpoint of easily achieving uniform heat treatment. The temperature rise rate during the heat treatment step is preferably 2 to 200°C / min, more preferably 5 to 150°C / min, and even more preferably 10 to 100°C / min. When the temperature rise rate is equal to or greater than the lower limit, it is easy to obtain the desired pore volume.

[0042] The heat treatment time is appropriately selected depending on the heat treatment temperature, the amount of inert gas supplied, etc. For example, it is 0.1 to 24 hours, more preferably 0.2 to 12 hours, and even more preferably 0.5 to 8 hours. When the heat treatment time is equal to or greater than the lower limit, carbonization tends to proceed sufficiently. When the heat treatment time is equal to or less than the upper limit, this is an appropriate time from the viewpoint of economy, and is therefore preferable. When heat treatment is carried out in multiple stages, the above heat treatment time refers to the total heat treatment time.

[0043] The inert gas, the amount of supply thereof, and the furnace used for the heat treatment may be the same as those used in step (2).

[0044] Alternatively, the phase separation step (2) and the carbonization step (3) may be carried out simultaneously. This can increase productivity. For example, the mixture obtained in step (1) may be heat-treated at 500 to 1300°C. In this case, the temperature rise in the carbonization step passes through 150 to 500°C, the temperature at which phase separation progresses, and the desired pore structure can be obtained. From the viewpoint of promoting phase separation, it is preferable to slow the rate of temperature rise up to the heat treatment temperature in step (3). Specifically, from the viewpoint of achieving both promotion of a phase-separated structure and improved productivity, the rate of temperature rise is preferably 2 to 100°C / min, more preferably 5 to 50°C / min, and even more preferably 10 to 30°C / min. In this case, the heat treatment time is, for example, 0.1 to 24 hours, more preferably 0.2 to 12 hours, and even more preferably 0.5 to 8 hours. However, from the viewpoint of further promoting a phase-separated structure, the phase separation step (2) and the heat treatment step (3) may be carried out independently.

[0045] <Step (4)> In step (4), calcium compounds are removed from the obtained carbide. This allows porous carbon to be obtained. The removal of calcium compounds is preferably carried out by acid washing. Examples of acids used in acid washing include hydrochloric acid, sulfuric acid, and nitric acid. Hydrochloric acid is preferred from the viewpoints that it easily dissolves metal compounds in the carbide, impurities such as sulfur are less likely to remain, and oxidation of the carbide is easily suppressed. The concentration of the acid used in acid washing may be changed appropriately depending on the type of acid used. For example, when hydrochloric acid is used, the concentration of hydrochloric acid is preferably 0.01 to 1.0 mol / L, more preferably 0.05 to 0.5 mol / L. A hydrochloric acid concentration within the above range is preferred because it makes it easy to remove metal compounds and is less likely to leave hydrochloric acid in the carbide.

[0046] The pH of the acid used during acid washing may be appropriately changed depending on the type, concentration, temperature, etc. of the acid used. The pH of the acid is preferably 3 or less, more preferably 2.5 or less. When the pH of the acid is the above upper limit or less, metal compounds can be easily and efficiently removed.

[0047] The acid washing may be carried out, for example, by immersing the obtained carbide in the acid. When the acid washing is carried out by immersion in acid, the mass ratio of the acid to the carbide may be adjusted appropriately depending on the type, concentration, temperature, etc. of the acid used. The mass of the carbide to be immersed relative to the mass of the acid is preferably 2 to 50 mass%, more preferably 5 to 30 mass%. When the mass ratio of the carbide to be immersed relative to the mass of the acid is within the above range, a sufficient washing effect is likely to be obtained.

[0048] The method for immersing the carbide in acid is not particularly limited. It may be a method in which acid is continuously added, retained for a predetermined time, and immersed while removing the acid, or a method in which the carbide is immersed in acid, retained for a predetermined time, drained, and then new acid is added, and the immersion-draining process is repeated. It may also be a method in which all or part of the acid is renewed. It may also be a method in which the acid is stirred during immersion.

[0049] The atmosphere in which the acid washing is carried out is not particularly limited and may be appropriately selected depending on the method used for washing. The acid washing is usually carried out in an air atmosphere.

[0050] The time for immersing the carbide in acid can be adjusted appropriately depending on the acid used, the treatment temperature, etc. The time for immersing the carbide in acid is preferably 1 to 60 minutes, more preferably 1 to 40 minutes, and even more preferably 1 to 35 minutes. When the time is equal to or greater than the lower limit, the metal compound can be easily removed sufficiently, and when the time is equal to or less than the upper limit, good productivity can be ensured.

[0051] After the carbonized product is acid-washed, it is preferable to remove the acid in the porous carbon by washing with water. This acid washing and water washing may be repeated until the calcium compounds in the porous carbon are removed to a desired extent. Furthermore, the temperature of the solution used in the acid washing and water washing is preferably high from the viewpoint of the efficiency of removing calcium compounds and residual acid, and is usually 60°C or higher.

[0052] In one embodiment of the present invention, when the phase-separated mixture is heat-treated in multiple stages, acid washing may be performed between the multiple heat treatments. For example, the phase-separated mixture in step (2) may be heat-treated (e.g., at 500 to 900°C), then acid-washed, and then heat-treated (e.g., at 900 to 1300°C).

[0053] After acid washing and water rinsing, the porous carbon may be subjected to a drying treatment using a known dryer such as a hot air dryer or a reduced pressure dryer. Drying is preferably carried out at a temperature of 50 to 150° C. A drying temperature within the above range is preferred because oxidation of the porous carbon is unlikely to occur and drying proceeds appropriately.

[0054] If necessary, the porous carbon after step (4) may be pulverized. By pulverization, the shape and particle size of the finally obtained porous carbon can be controlled to the desired shape and particle size. The pulverization method is not particularly limited. For example, known pulverizers such as a ball mill, centrifugal roll mill, ring roll mill, centrifugal ball mill, jet mill, cone crusher, double roll crusher, disc crusher, and rotary crusher can be used alone or in combination.

[0055] The method for producing porous carbon may further include a classification step after the pulverization step. For example, porous carbon with a narrow particle size distribution can be obtained by removing particles that are significantly smaller or larger than the desired particle size. The classification method is not particularly limited. Examples of classification methods include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertia classification, hydraulic classification, centrifugal classification, etc. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, centrifugal classification, etc. From an economical standpoint, it is preferable to use a dry classifier. To prevent surface oxidation during pulverization, it is preferable to perform the pulverization step and classification step in an inert gas atmosphere.

[0056] Pulverization and classification can also be performed using a single device. For example, pulverization and classification can be performed using a jet mill equipped with a dry classification function. Furthermore, devices having a pulverizer and a classifier independent from each other can also be used. In this case, pulverization and classification can be performed continuously, or can be performed discontinuously.

[0057] In another embodiment, the porous carbon of the present invention can be produced by a method comprising, for example, the steps of: (1) obtaining a mixture containing a carbon source and an alkaline earth metal oxide as a pore source, or preparing a metal organic acid; (2) heat-treating the mixture or the metal organic acid in an inert gas atmosphere to obtain a carbide; (3) removing the alkaline earth metal oxide from the carbide when a carbon source and an alkaline earth metal oxide are used, or removing the metal oxide when a metal organic acid is used, to obtain porous carbon; and (4) optionally, pulverizing the porous carbon.

[0058] <Step (1)> The carbon source is preferably not particularly limited. Various organic polymers, thermoplastic resins, and thermosetting resins can be used as the carbon source. Specific examples include various synthetic resins or polymers such as polyvinyl alcohol, aliphatic or aromatic polyester resins, polyolefin resins, acrylic resins, styrene resins, polyamide resins, polyacrylonitrile resins, and elastomers mainly composed of polybutadiene and / or polyisoprene, as well as thermoplastic resin polymers such as natural rubber and petroleum resins, and thermosetting resins such as phenolic resins, furan resins, epoxy resins, and alkyd resins. These resins or polymers can be used alone or in combination of two or more. Among these, polyvinyl alcohol is preferred from the viewpoint of its ability to adjust the pore volume.

[0059] The pore source (template particle) is not particularly limited. Examples of the pore source include alkaline earth metal oxides. Examples of alkaline earth metals include magnesium, calcium, strontium, and barium. Among these, magnesium and calcium are preferred, and magnesium is particularly optimal.

[0060] The shape and size of the pore source are not particularly limited. The shape may be, for example, particulate, scale-like, layer-like, etc., but is preferably particulate. In this case, the average particle size (diameter) of the pore source is preferably 3 to 300 nm, more preferably 5 to 200 nm, even more preferably 7 to 100 nm, still more preferably 8 to 50 nm, and particularly preferably 9 to 30 nm.

[0061] The method for mixing the carbon source and the alkaline earth metal oxide is not particularly limited, and they can be mixed by any mixing method.

[0062] The amount of alkaline earth metal oxide mixed with the carbon source is preferably 50 to 300 parts by mass, more preferably 80 to 250 parts by mass, and even more preferably 90 to 150 parts by mass, per 100 parts by mass of the carbon source. When the amount of alkaline earth metal oxide is within this range, the relationship between the mass transfer coefficient and the relative pressure, and the pore volume of the resulting porous carbon can be favorable.

[0063] Instead of a mixture containing a carbon source and an alkaline earth metal oxide, a metal organic acid that functions as both a carbon source and a pore source may be used. Examples of the metal organic acid include magnesium citrate, magnesium oxalate, calcium citrate, and calcium oxalate. The metal organic acid may be a hydrate or an anhydrous form.

[0064] <Step (2)> In step (2), the mixture obtained in step (1) or the metal organic acid is heat-treated in an inert gas atmosphere to obtain a carbide. Examples of inert gases include nitrogen, argon, and mixtures thereof. The lower the concentration of the oxidizing gas in the gas used, the better. The concentration of the oxidizing gas, particularly oxygen, is typically 1% by volume or less, more preferably 0.1% by volume or less, based on the volume of the gas used. When the concentration of the oxidizing gas is below the upper limit, oxidation of the mixture is suppressed, making it easier to obtain a structure with the desired characteristics. Furthermore, oxidative decomposition of the resulting structure can be suppressed. The supply (flow) rate of the inert gas is typically 200 to 7,000 mL / min, preferably 500 to 6,000 mL / min, and more preferably 1,000 to 5,000 mL / min per gram of mixture.

[0065] The heat treatment temperature is preferably 500 to 1300°C, more preferably above 550°C to 1200°C, even more preferably 600 to 1100°C, and particularly preferably 650 to 1000°C. By heat treating the mixture obtained in step (1) or the metal organic acid in an inert gas atmosphere, preferably at a temperature within the above range, the relationship between the mass transfer coefficient and the relative pressure, and the pore volume of the resulting porous carbon can be optimized. Furthermore, this facilitates removal of the metal oxide from the subsequent step of removing the metal oxide from the carbide.

[0066] The temperature rise rate during the heat treatment step is preferably 2°C / min or more, and although there is no particular upper limit, it is preferably 200°C / min or less from the viewpoint of easily achieving uniform heat treatment. The temperature rise rate during the heat treatment step is preferably 2 to 200°C / min, more preferably 5 to 150°C / min, and even more preferably 10 to 100°C / min. When the temperature rise rate is equal to or greater than the lower limit, it is easy to obtain the desired pore volume.

[0067] The heat treatment time is appropriately selected depending on the heat treatment temperature, the amount of inert gas supplied, etc. For example, it is 0.1 to 24 hours, more preferably 0.2 to 12 hours, and even more preferably 0.5 to 8 hours. When the heat treatment time is equal to or greater than the lower limit, carbonization tends to proceed sufficiently. When the heat treatment time is equal to or less than the upper limit, it is an appropriate time from the viewpoint of economy, and is therefore preferred.

[0068] The heat treatment may be performed using various furnaces such as rotary kilns, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and moving bed furnaces, as well as various dryers such as spray dryers, moving dryers, agitator dryers, roll dryers, and thin film evaporators. A continuous furnace or dryer may be used, which continuously introduces the material to be heat-treated and removes the material after heat treatment, or a batch furnace or dryer may be used, which does so discontinuously. The heating means may be any means capable of heating to a predetermined temperature, such as electric heating, gas combustion heating, microwave heating, high-frequency induction heating, or electrical heating. These heating means may be used alone or in combination.

[0069] <Step (3)> In step (3), metal oxides are removed from the obtained carbide. This allows porous carbon to be obtained. The removal of metal oxides is preferably carried out by acid washing. Examples of acids used in acid washing include common inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and acetic acid. The concentration of the acid used in acid washing may be changed appropriately depending on the type of acid used. For example, the acid concentration is preferably 0.01 to 2 mol / L, more preferably 0.05 to 1 mol / L. An acid concentration within the above range is preferable because it makes it easy to remove metal oxides and makes it less likely that acid will remain in the carbide.

[0070] The pH of the acid used during acid washing may be appropriately changed depending on the type, concentration, temperature, etc. of the acid used. The pH of the acid is preferably 3 or less, more preferably 2.5 or less. When the pH of the acid is the above upper limit or less, metal oxides can be easily removed efficiently.

[0071] The acid washing may be carried out, for example, by immersing the obtained carbide in the acid. When the acid washing is carried out by immersion in acid, the mass ratio of the acid to the carbide may be adjusted appropriately depending on the type, concentration, temperature, etc. of the acid used. The mass of the carbide to be immersed relative to the mass of the acid is preferably 2 to 50 mass%, more preferably 5 to 30 mass%. When the mass ratio of the carbide to be immersed relative to the mass of the acid is within the above range, a sufficient washing effect is likely to be obtained.

[0072] The method for immersing the carbide in acid is not particularly limited. It may be a method in which acid is continuously added, retained for a predetermined time, and immersed while removing the acid, or a method in which the carbide is immersed in acid, retained for a predetermined time, drained, and then new acid is added, and the immersion-draining process is repeated. It may also be a method in which all or part of the acid is renewed. It may also be a method in which the acid is stirred during immersion.

[0073] The atmosphere in which the acid washing is carried out is not particularly limited and may be appropriately selected depending on the method used for washing. The acid washing is usually carried out in an air atmosphere.

[0074] The time for immersing the carbide in acid can be adjusted appropriately depending on the acid used, the treatment temperature, etc. The time for immersing the carbide in acid is preferably 1 to 60 minutes, more preferably 1 to 40 minutes, and even more preferably 1 to 35 minutes. When the time for immersing the carbide in acid is equal to or greater than the above-mentioned lower limit, the metal oxide can be easily removed sufficiently, and when it is equal to or less than the above-mentioned upper limit, good productivity can be ensured.

[0075] After the carbide is acid-washed, it is preferable to remove the acid in the porous carbon by washing with water. This acid washing and water washing may be repeated until the metal oxides in the porous carbon are removed to a desired extent. Furthermore, the temperature of the solution used in the acid washing and water washing is preferably high from the viewpoint of the efficiency of removing the metal oxides and residual acid, and is usually 60°C or higher.

[0076] After acid washing and water rinsing, the porous carbon may be subjected to a drying treatment using a known dryer such as a hot air dryer or a reduced pressure dryer. Drying is preferably carried out at a temperature of 50 to 150° C. A drying temperature within the above range is preferred because oxidation of the porous carbon is unlikely to occur and drying proceeds appropriately.

[0077] If necessary, the porous carbon after step (3) may be pulverized. By pulverization, the shape and particle size of the finally obtained porous carbon can be controlled to the desired shape and particle size. The pulverization method is not particularly limited. For example, known pulverizers such as a ball mill, centrifugal roll mill, ring roll mill, centrifugal ball mill, jet mill, cone crusher, double roll crusher, disc crusher, and rotary crusher can be used alone or in combination.

[0078] The method for producing porous carbon may further include a classification step after the pulverization step. For example, porous carbon with a narrow particle size distribution can be obtained by removing particles that are significantly smaller or larger than the desired particle size. The classification method is not particularly limited. Examples of classification methods include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertia classification, hydraulic classification, centrifugal classification, etc. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, centrifugal classification, etc. From an economical standpoint, it is preferable to use a dry classifier. To prevent surface oxidation during pulverization, it is preferable to perform the pulverization step and classification step in an inert gas atmosphere.

[0079] Pulverization and classification can also be performed using a single device. For example, pulverization and classification can be performed using a jet mill equipped with a dry classification function. Furthermore, devices having a pulverizer and a classifier independent from each other can also be used. In this case, pulverization and classification can be performed continuously, or can be performed discontinuously.

[0080] <Solid Acidic Gas Absorbent> The porous carbon of the present invention has a characteristic pore structure and can be suitably used as a carrier for a solid acidic gas absorbent. Therefore, the present invention also covers a solid acidic gas absorbent comprising the porous carbon of the present invention and an acidic gas absorbent, in which the acidic gas absorbent is impregnated into the porous carbon. Examples of acidic gases include carbon dioxide, SO ｘ and NO ｘExamples of acidic gas absorbents corresponding to these include amine compounds; Cu—Zr composite oxides; Fe—Zr composite oxides; Ni—Zr composite oxides; and agents containing, as a main component, at least one selected from the group consisting of oxides of Li, Na, K, Rb, Cs, Ca, Mg, Sr, and Ba, and at least one selected from the group consisting of oxides of Ti, Si, Al, and Zr. These acidic gas absorbents can be used alone or in combination of two or more. The porous carbon of the present invention can be sufficiently impregnated with an acidic gas absorbent, and the solid acidic gas absorbent of the present invention allows acidic gases to move smoothly through the pores, even though a sufficient amount of acidic gas absorbent is impregnated. Therefore, the solid acidic gas absorbent of the present invention can achieve an excellent acidic gas adsorption / desorption rate and a high acidic gas adsorption / desorption amount in a short period of time.

[0081] The amine compound is not particularly limited. Since amine groups react with carbon dioxide, all amine compounds can be used. Those with high reactivity with carbon dioxide are particularly preferred, and for example, those containing as many primary, secondary, and tertiary amine groups as possible in one molecule are more preferred. Furthermore, in the present invention, it is assumed that carbon dioxide is adsorbed by the amine compound and then decomposed and released, and the solid carbon dioxide absorbent is repeatedly used. Therefore, a compound with a relatively high boiling point is preferred to prevent the amine compound from being released when the carbon dioxide is decomposed and released. From these points of view, an amine compound with a molecular weight per N atom of 110 or less and a boiling point of 100°C or higher is preferred. Amine compounds having a boiling point of less than 100°C and a molecular weight per N atom of 110 or less include, for example, ethylamine (boiling point 38°C, molecular weight per N atom 45.1), triethylamine (boiling point 89.7°C, molecular weight per N atom 101), isopropylamine (boiling point 32.4°C, molecular weight per N atom 59.4), and t-butylamine (boiling point 45.0°C, molecular weight per N atom 73.1), many of which have a strong odor and are toxic and therefore unsuitable for the present invention. From these points of view, amine compounds having a molecular weight per N atom of 110 or less and a boiling point of 100°C or higher are preferred. Preferred examples of such amine compounds include alkanolamines such as monoethanolamine, diisopropanolamine, diethanolamine, and β-amine ethylethanolamine; ethyleneamines such as triethylenediamine, triethylenepentamine, tetraethylenepentamine, pentaethylenehexamine, triethylenetetraamine, linear polyethyleneimine, branched polyethyleneimine, polyvinylamine, and chitosan; aliphatic amines such as hexamethylenediamine and iminobispropylamine; and alicyclic amines such as imidazole and piperazine. These amine compounds may be used alone or in combination of two or more. The amine impregnation rate in the solid absorbent carrier is preferably 15 to 70% by mass based on the total mass of the solid absorbent carrier and the amine.If the amine impregnation rate is within the above range, a sufficient amount of amine is impregnated, and there is a large amount of amine that functions as a carbon dioxide absorbent, so that the material can be used as a solid absorbent with high utilization efficiency, which is preferable.

[0082] The method for impregnating the porous carbon for use as a solid absorbent carrier with an amine is not particularly limited. Suitable known methods include, for example, a method in which a solution of an amine compound dissolved in a suitable solvent is sprayed onto the porous carbon, or a method in which the porous carbon for use as a solid absorbent carrier is immersed in an aqueous solution of the amine compound to allow the amine to be sufficiently adsorbed, and then dried to prepare the porous carbon. In one embodiment, a preferred method is to immerse the porous carbon in an aqueous solution of the amine compound to allow the amine to be sufficiently adsorbed, and then dried under reduced pressure to prepare the porous carbon.

[0083] The method for impregnating the porous carbon for use as a solid absorbent carrier with an acidic gas absorbent other than an amine compound is not particularly limited. Suitable known methods include, for example, a method in which a solution of the acidic gas absorbent dissolved in a suitable solvent or a dispersion of the acidic gas absorbent dispersed in a suitable solvent is sprayed onto the porous carbon, or a method in which the porous carbon for use as a solid absorbent carrier is immersed in an aqueous solution of the acidic gas absorbent or a dispersion of the acidic gas absorbent to sufficiently adsorb the acidic gas absorbent, and then dried to prepare the porous carbon.

[0084] <Method for Separating and Recovering Acidic Gases> The present invention also relates to a method for separating and recovering acidic gases using the solid acidic gas absorbent. The method of the present invention includes an absorption step in which a gas to be treated is brought into contact with the solid absorbent to absorb the acidic gas, and a desorption step in which the acidic gas absorbed in the absorption step is desorbed from the solid acidic gas absorbent. The desorption step includes at least one step selected from the group consisting of (A) applying a reduced pressure to the solid acidic gas absorbent, (B) contacting the solid acidic gas absorbent with an inert gas that does not contain acidic gas, and (C) heating the solid acidic gas absorbent.

[0085] The gas to be treated contains an acidic gas. The acidic gas content and temperature in the gas to be treated in the absorption step are not particularly limited as long as they are conditions that the solid acidic gas absorbent can withstand, but may be, for example, an acidic gas partial pressure of 100 kPa or less and a temperature of 20 to 60°C. When the acidic gas is carbon dioxide, specific examples of the conditions include the usage conditions expected in thermal power plants and the like (carbon dioxide partial pressure: 7 to 100 kPa, temperature: 40 to 60°C) and the usage conditions expected in space stations and the like (carbon dioxide partial pressure: 0 to 1 kPa, temperature: 20 to 25°C). The gas to be treated may be at atmospheric pressure or pressurized.

[0086] In the method of the present invention, by using the above-mentioned solid absorbent, it is possible to achieve an excellent acid gas adsorption rate and a high acid gas adsorption amount in a short time. In the method of the present invention, from the viewpoint of efficiently absorbing acid gases from the gas to be treated, it is very useful for the solid absorbent of the present invention to have an excellent acid gas adsorption rate and a high acid gas adsorption amount in a short time.

[0087] In the above-mentioned desorption step (A), when acidic gases are desorbed from the solid acidic gas absorbent by applying a reduced pressure, the pressure is preferably reduced to about 0.01 to 0.5 Pa, and from the viewpoint of the amount of acidic gas desorbed and the stability of the solid acidic gas absorbent, the pressure is preferably reduced to 0.01 to 0.25 Pa. The solid acidic gas absorbent or a container containing the same may be heated during depressurization. When heating, the temperature may be about 20 to 60°C, and in this case, the pressure is preferably reduced to 0.01 to 0.55 Pa. When acidic gases are desorbed from the solid acidic gas absorbent by applying a reduced pressure, the temperature of the gas to be treated is preferably 20 to 60°C, and the acidic gas partial pressure is preferably 100 kPa or less.

[0088] In the desorption step, when the acidic gas is desorbed from the solid acidic gas absorbent by contacting the solid acidic gas absorbent with (B) an inert gas that does not contain the acidic gas, the partial pressure of the acidic gas can be reduced by contacting the solid acidic gas absorbent with the inert gas that does not contain the acidic gas, and the acidic gas can be desorbed. Examples of the inert gas include argon and nitrogen.

[0089] In the case where the acidic gas is desorbed from the solid acidic gas absorbent by heating in the desorption step (C), the acidic gas can be desorbed by increasing the temperature from the temperature during acidic gas absorption. In this case, the temperature during acidic gas absorption and the temperature during acidic gas desorption may be, for example, 10 to 40°C or 20 to 25°C for the temperature during acidic gas absorption, and about 60 to 90°C for the temperature during acidic gas desorption.

[0090] The solid absorbent of the present invention has a particularly excellent short-term acid gas desorption rate and a high acid gas desorption amount, because the porous carbon can be impregnated with a sufficient amount of acid gas absorbent and has a pore structure that can maintain pores that allow acid gases to move smoothly even after the acid gas absorbent is impregnated. In methods for separating and recovering acid gases, it is generally assumed that separation and recovery will be performed repeatedly. From the perspective of efficiency in separation and recovery of acid gases, an excellent short-term desorption rate and a large desorption amount are very useful.

[0091] <Acid Gas Separation and Recovery System> The present invention also relates to an acid gas separation and recovery system comprising the above-mentioned solid acid gas absorbent. The acid gas separation and recovery system is not particularly limited except that it uses the solid absorbent of the present invention. Examples of acid gas separation and recovery systems comprising a solid absorbent include a fixed-bed acid gas separation and recovery system in which the gas to be treated is alternately introduced into two containers filled with solid absorbents, and the acid gas is continuously recovered by alternately absorbing the acid gas and regenerating the solid absorbent, and a moving-bed gas separation and recovery system in which the solid absorbent moves within the system using a conveyor, honeycomb rotor / container, etc., absorbs the acid gas from the gas to be treated in the absorption zone, and releases and recovers the absorbed acid gas in the regeneration zone.

[0092] One embodiment of a fixed-bed acid gas separation and recovery system is a semi-batch process system that includes three towers, each of which alternates between the three processes of absorption, scrubbing, and regeneration. Focusing on one of the towers, the gas to be treated is supplied to the tower during the absorption process, where the acid gas is absorbed. Simultaneously, another tower performs a scrubbing process, where acid gas is supplied to the tower. This flushes out the gas remaining in the interstices within the tower, thereby increasing the acid gas purity of the recovered gas during the regeneration process. The remaining tower then performs a regeneration process, where acid gas is desorbed from the solid acid gas absorbent by one or more of the following methods: (A) applying a reduced pressure, (B) contacting an inert gas containing no acid gas, and (C) heating. The three towers perform their respective processes without overlapping with each other, and switch between them at regular intervals. This allows for continuous acid gas recovery overall, despite each tower operating in a batch manner. In the fixed bed acidic gas separation and recovery system, the form and use of the solid absorbent are not particularly limited, but it is preferably in a form that can be packed into a fixed bed, such as granular, honeycomb, or plate form.

[0093] The moving-bed acidic gas separation and recovery system includes an absorption tank, a desorption tank, and a transport means for transporting a solid absorbent from the outlet of the desorption tank to the inlet of the absorption tank. The absorption tank includes a feed port for introducing the solid absorbent into the absorption tank, a discharge port for discharging the solid absorbent that has absorbed acidic gases from the absorption tank, a feed port for introducing the gas to be treated into the absorption tank, and a discharge port for discharging the gas to be treated (off-gas) from which the acidic gases have been separated and removed from the absorption tank. The desorption tank includes a feed port for supplying the solid absorbent that has absorbed acidic gases to the desorption tank, a discharge port for discharging the solid absorbent from which the acidic gases have been separated and recovered from the supplied solid absorbent, and a discharge port for discharging the acidic gases separated from the solid absorbent from the desorption tank. The desorption tank includes one or more pieces of equipment selected from the group consisting of equipment for reducing the pressure inside the tank, equipment for introducing an inert gas that does not contain acidic gases into the tank, and equipment for heating the inside of the tank. Corresponding to these facilities, the desorption tank performs one or more of the following operations selected from the group consisting of (A) applying a pressure reduction to the solid acidic gas absorbent, (B) contacting the solid acidic gas absorbent with an inert gas that does not contain acidic gas, and (C) heating the solid acidic gas absorbent. Equipment for reducing the pressure inside the tank includes, for example, a vacuum pump and an inlet port connected to the vacuum pump and provided in the desorption tank. Equipment for introducing an inert gas that does not contain acidic gas into the tank includes, for example, an inert gas cylinder, an inert gas inlet connected to the inert gas cylinder and provided in the desorption tank, and an outlet for discharging the inert gas that has been contacted with the solid acidic gas absorbent from the desorption tank. Equipment for heating the solid acidic gas absorbent includes, for example, a heater.

[0094] One embodiment of a moving-bed acid gas separation and recovery system includes a hopper arranged vertically downward, an absorption tower where an absorption process is performed, a desorption tower (regeneration tower) where a desorption process is performed, a drying tower where a solid absorbent is dried, a cooling tower where the solid absorbent is cooled, and a conveyor that transfers the solid absorbent from the cooling tower to the hopper. The solid acid gas absorbent stored in the hopper moves under its own weight through the absorption tower, desorption tower, drying tower, and cooling tower in that order, and is transported from the cooling tower to the hopper by the conveyor. In the absorption tower and desorption tower, a moving bed is formed by the solid acid gas absorbent descending within the tower and the gas ascending within each treatment tower (see, for example, JP 2013-121562 A).

[0095] Another embodiment of the moving bed acidic gas separation and recovery system includes an absorption tank having a moving layer formed therein by a solid absorbent material, and a desorption tank having a moving layer formed therein by the solid absorbent material that has passed through the absorption tank. The absorption tank has a treated gas supply port at the bottom through which a treated gas containing an acidic gas is supplied, and an off-gas outlet at the top of the absorption tank for discharging the off-gas resulting from the acidic gas being absorbed and removed by the solid absorbent. The desorption tank has a steam supply port at the bottom through which steam for desorption is supplied, and an acidic gas outlet at the top of the desorption tank for discharging the acidic gas desorbed from the solid absorbent (see, for example, JP 2018-187574 A).

[0096] In yet another embodiment of a moving-bed acid gas separation and recovery system, the system includes a rotating honeycomb rotor as a means for moving the solid absorbent. The honeycomb rotor carrying the solid absorbent rotates within a sealed casing that is divided into an absorption zone and a desorption zone. In the absorption zone, the gas to be treated is passed through the honeycomb rotor, and the acid gas is absorbed by the solid absorbent supported on the honeycomb rotor, thereby removing the acid gas from the gas to be treated. The honeycomb rotor moves to the desorption zone as the rotor rotates, and the acid gas absorbed by the solid absorbent is desorbed. In the desorption tank, the solid acid gas absorbent is subjected to one or more of the following processes selected from the group consisting of (A) applying a reduced pressure, (B) contacting with an inert gas that does not contain acid gas, and (C) heating, thereby desorbing the acid gas from the solid absorbent. The absorption and desorption processes are carried out continuously as the rotor continues to rotate.

[0097] A system including a rotating honeycomb rotor as a means for transporting a solid absorbent material includes a honeycomb rotor, a casing, a gas circulation circuit, and at least one selected from the group consisting of a gas heater, a saturated steam generator heater, a pressure reducing device, and an inert gas supply device, and the solid absorbent material is supported on the honeycomb rotor. Examples of systems including a rotating honeycomb rotor include those described in Japanese Patent No. 7036414 and Japanese Patent Application Laid-Open No. 2019-171256. For example, in existing systems including a rotating honeycomb rotor as a means for transporting a solid absorbent material, the rotation time of the honeycomb rotor and the time required to pass through the absorption zone and desorption zone vary depending on the diameter and volume of the honeycomb rotor. In one embodiment, the honeycomb rotor makes one rotation in approximately 3 to 5 minutes. The rotating honeycomb rotor passes through the absorption zone in approximately 30 to 180 seconds. The honeycomb rotor itself may be made, for example, from non-combustible paper such as ceramic paper or metal by corrugating. The solid absorbent material may be supported by applying or spraying a dispersion containing the solid absorbent material and a binder onto the honeycomb rotor.

[0098] The porous carbon of the present invention can be sufficiently impregnated with an acidic gas absorbent, and the solid acidic gas absorbent of the present invention maintains pores that allow the acidic gas to move smoothly through the pores, even though a sufficient amount of the acidic gas absorbent is impregnated therein. Therefore, an acidic gas separation and recovery system including the solid absorbent of the present invention can particularly achieve an excellent acidic gas adsorption / desorption rate and a high amount of acidic gas adsorption / desorption in a short period of time.

[0099] The present invention will be specifically described below with reference to examples, but these examples are not intended to limit the scope of the present invention.

[0100] [Analysis Method] <Pore Volume of 2 nm or More and 200 nm or Less by Nitrogen Adsorption Method> For the porous carbon or solid absorbent, the adsorption isotherm obtained by measuring the amount of nitrogen adsorbed was analyzed by the BJH method, and the volume of pores having a pore size (pore diameter) of 2 nm or more and 200 nm or less was calculated.

[0101] <Pore Volume of 2 nm or Less by Nitrogen Adsorption Method> For porous carbon or solid absorbent, the adsorption isotherm obtained by measuring the amount of adsorbed nitrogen was analyzed by the QS-DFT method, and the volume of pores having a pore diameter of 2 nm or less (pore diameter) was calculated as the micropore volume. The ratio (micropore ratio) of the pore volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the pore volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the pore volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method was calculated using the following formula:

[0102] <Mass Transfer Coefficient by Nitrogen Adsorption Method> A sample tube was filled with porous carbon, which was the measurement sample. This sample tube was placed in an "Autosorb-iQ-MP" manufactured by Quantachrome, and the pressure was reduced once while the tube was cooled to -196°C. Nitrogen (purity 99.999%) was then adsorbed onto the measurement sample at a predetermined relative pressure. The amount of nitrogen adsorbed onto the sample when equilibrium pressure was reached at each predetermined relative pressure was measured, and an adsorption isotherm was created. The mass transfer coefficient was determined by analyzing the data of the created nitrogen adsorption isotherm. Specifically, the pressure change of nitrogen until adsorption equilibrium was reached at each predetermined relative pressure was converted into a mass transfer coefficient using the LDF approximation. At this time, the relative pressure was 1.0 x 10－４ Above 1.0 x 10 －３ The following ranges were converted to mass transfer coefficients so that the number of plots was at least 5: Relative pressure (P / P ０ A graph was created with the relative pressure 1.0 × 10) on the x-axis and the mass transfer coefficient on the y-axis. －４ Above 1.0 x 10 －３ An approximate straight line was drawn within the following range, and its slope (a) was determined.

[0103] <Bulk Density> The bulk density was measured using a Powder Tester PT-X manufactured by Hosokawa Micron Corp. A sample was placed in an automatic tap density measuring unit, and the bulk density was calculated from the volume after tapping 3,000 times.

[0104] <Production of Porous Carbon> [Example 1] 1.0 g of glucose (sold by Fujifilm Wako Pure Chemical Industries, Ltd.), 3 g of calcium chloride dihydrate (300 parts by weight per 100 parts by weight of glucose), and 1.5 g of ion-exchanged water (150 parts by weight per 100 parts by weight of glucose) were mixed. The resulting mixture was heated to 700°C at a heating rate of 10°C / min under a nitrogen gas flow of 1250 mL / min per 1 g of mixture, and heat-treated at this temperature for 60 minutes to obtain a carbonized product. The carbonized product was immersed in 0.1 mol / L hydrochloric acid and washed by stirring at 80°C for 30 minutes, and then removed onto a Buchner funnel. Water washing was performed until the pH of the filtrate reached a range of 6 to 8. Acid washing and water washing were repeated three times, followed by hot air drying at 80°C to obtain particulate porous carbon 1.

[0105] Example 2 Particulate porous carbon 2 was obtained in the same manner as in Example 1, except for the changes shown in Table 1.

[0106] Example 3: 1 g of polyvinyl alcohol (PVA: Kuraray Poval 28-98, manufactured by Kuraray Co., Ltd.) was mixed with 1 g of magnesium oxide particles having an average particle size of 10 nm (100 parts by mass per 100 parts by mass of PVA). The resulting mixture was heated to 700°C at a heating rate of 10°C / min in a nitrogen gas flow of 1250 mL / min per 1 g of mixture, and heat-treated at this temperature for 60 minutes to obtain a carbonized product. The carbonized product was immersed in 1 mol / L sulfuric acid and washed by stirring at 80°C for 30 minutes, and then removed onto a Buchner funnel. Water washing was carried out until the pH of the filtrate reached a range of 6 to 8. Acid washing and water washing were repeated three times, followed by hot air drying at 80°C to obtain particulate porous carbon 3.

[0107] Comparative Example 1 Kuraray Coal GLC manufactured by Kuraray Co., Ltd. was used as the porous carbon 4 .

[0108]

[0109]

[0110] A solid acidic gas absorbent was produced by impregnating the porous carbon with an acidic gas absorbent. To select the appropriate impregnation amount for each porous carbon, the amount of amine impregnated was varied to produce solid absorbents, and the carbon dioxide adsorption rate and amount of carbon dioxide adsorbed were measured.

[0111] [Example 4-1] 10 g of methanol was weighed into a 50 mL sample tube, and 10.0 g of polyethyleneimine (average molecular weight approximately 600) (sold by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto, followed by stirring at room temperature to prepare a 50 mass % amine solution. 0.5 g of porous carbon 1 was weighed into a zippered plastic bag, and 1.5 mL of a 50 mass % amine solution was added thereto. While heating this to 60°C in a vacuum constant temperature dryer (manufactured by EYELA), the pressure inside the zippered plastic bag was reduced to 0.03 MPa to remove the methanol solvent, thereby obtaining a solid absorbent 1-1 in which the amine was impregnated onto the porous carbon 1. The amine impregnation rate was calculated using the mass of the porous carbon (W １ ) and the mass of the solid absorber (W ２ The mass change was calculated from the mass change of the

[0112] Examples 4-2 to 4-5 Solid absorbents 1-2 to 1-5 were obtained in the same manner as in Example 4-1, except that the amine impregnation conditions were changed as shown in Table 3.

[0113] Comparative Example 2-1 A solid absorbent 4-1 was obtained in the same manner as in Example 4-1, except that porous carbon 1 was changed to porous carbon 4 and the amine impregnation conditions were changed as shown in Table 3.

[0114] Comparative Examples 2-2 to 2-5 Solid absorbents 4-2 to 4-5 were obtained in the same manner as in Comparative Example 2-1, except that the amine impregnation conditions were changed as shown in Table 3.

[0115] <Carbon dioxide adsorption amount per 1 g of solid absorbent> The carbon dioxide adsorption amount was measured using a thermogravimetric analyzer (TGA-51, manufactured by Shimadzu Corporation). 5 to 100 mg of the solid absorbent was weighed out according to the size of the pan and added to the pan. Next, the solid absorbent was dried in the thermogravimetric analyzer under a nitrogen flow at 70°C for 60 minutes until it reached a constant weight, and then cooled to 30°C. The mass at this time was defined as the post-drying mass (W dry Then, 15% by mass carbon dioxide gas was flowed into the thermogravimetric analyzer at a rate of 4.2 L / min, and the carbon dioxide was adsorbed into the solid absorbent at 30°C for 2 hours. The mass after the first 60 seconds of adsorption during the 2 hours was taken as the post-adsorption mass (W abs60 The carbon dioxide adsorption amount (mg / g) per 1 g of the solid absorbent after 60 seconds of adsorption was calculated from the mass after drying and the mass after adsorption using the following formula:

[0116] <Carbon dioxide adsorption rate per 1 g of solid absorbent> In the measurement of the carbon dioxide adsorption amount, the carbon dioxide adsorption rate per 1 g of solid absorbent after 60 seconds of adsorption was calculated by differentiating the carbon dioxide adsorption amount after 60 seconds of adsorption with respect to time.

[0117] <Amount of carbon dioxide desorbed per 1 g of solid absorbent> As described above, the mass of the solid absorbent after adsorbing carbon dioxide at 30°C for 2 hours was determined as the mass after adsorption measurement (W abs) was used. Two hours was adopted as the time until the amount of carbon dioxide adsorption reached a state close to saturation. The solid absorbent material after the carbon dioxide adsorption measurement was heated to 70°C under a nitrogen flow in a thermogravimetric analyzer (TGA-51 manufactured by Shimadzu Corporation) to desorb carbon dioxide. The mass after desorption for 60 seconds was defined as the post-desorption mass (W ｄｅｓ60 ) The mass after desorption (W ｄｅｓ60 ) and the mass after adsorption measurement (W abs ) and the amount of carbon dioxide desorbed per 1 g of solid absorbent after 60 seconds of desorption (mg / g) was calculated using the following formula.

[0118] <Carbon dioxide desorption rate per 1 g of solid absorbent> In the carbon dioxide desorption measurement, the carbon dioxide desorption rate per 1 g of solid absorbent after 60 seconds of desorption was calculated by differentiating the amount of carbon dioxide desorbed with time after 60 seconds of desorption.

[0119] The carbon dioxide adsorption amounts for each of the solid absorbents 1-1 to 1-5 and 4-1 to 4-5 are shown in Figure 2, and the carbon dioxide adsorption rates are shown in Figure 3. The amine impregnation amounts of solid absorbents 1-3 and 4-3, which showed excellent carbon dioxide adsorption amounts and carbon dioxide adsorption rates when the amine impregnation amount was increased, were designated as the representative amine impregnation rates of porous carbon 1 and porous carbon 4, respectively.

[0120]

[0121] [Examples 5-6] In addition to porous carbons 1 and 4, porous carbons 2 and 3 were also prepared by varying the amine impregnation amount. The representative amine impregnation ratio of each porous carbon was determined in the same manner as for porous carbon 1. For each solid absorbent having a representative amine impregnation ratio, the carbon dioxide adsorption rate per gram of solid absorbent after 60 seconds of adsorption [mg / (g min)], the carbon dioxide adsorption amount per gram of solid absorbent after 60 seconds of adsorption [mg / g], the carbon dioxide desorption rate per gram of solid absorbent after 60 seconds of desorption [mg / (g min)], and the carbon dioxide desorption amount per gram of solid absorbent after 60 seconds of desorption [mg / g] were determined. The results are shown in Table 4. Furthermore, the pore volume and micropore ratio of 2 nm to 200 nm were determined for each solid absorbent. Solid absorbents 2 and 3 were prepared in the same manner as in Example 4-1, except that the preparation conditions were changed to those shown in Table 4.

[0122]

[0123] When used as a support for a solid absorbent for acidic gases, the porous carbon of the present invention can achieve an excellent carbon dioxide adsorption / desorption rate and a high carbon dioxide adsorption / desorption amount in a short period of time, and therefore can be suitably used as a support for a solid absorbent for acidic gases.

Claims

1. The pore volume of pores with diameters of 2 nm to 200 nm calculated from the nitrogen adsorption isotherm using the BJH method is 0.7 cm ３ / g or more, and the ratio of the pore volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the pore volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the pore volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method from a nitrogen adsorption isotherm is 45% or less.

2. In measuring the nitrogen adsorption isotherm, the pressure change of nitrogen until adsorption equilibrium is reached at each specified relative pressure is converted into a mass transfer coefficient using the LDF approximation. －４ Above 1.0 x 10 －３ 2. The porous carbon according to claim 1, wherein the slope of an approximate line obtained by linearly approximating the relationship between the relative pressure and the mass transfer coefficient in the following formula is 0.95 or more.

3. Bulk density is 0.17 g / cm ３ 2. The porous carbon of claim 1, wherein:

4. The porous carbon according to claim 1, wherein the acid gas is carbon dioxide.

5. A solid acid gas absorbent comprising the porous carbon of claim 1 and an acid gas absorbent, wherein the acid gas absorbent is impregnated into the porous carbon.

6. The solid acid gas absorbent according to claim 5, wherein the acid gas absorbent is an amine compound.

7. The pore volume of pores with diameters of 2 nm to 200 nm calculated from the nitrogen adsorption isotherm using the BJH method is 0.7 cm ３ / g or more, and the ratio of the pore volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method to the sum of the pore volume of pores with a diameter of 2 nm or more and 200 nm or less calculated by the BJH method and the pore volume of pores with a diameter of 2 nm or less calculated by the QS-DFT method from the nitrogen adsorption isotherm is 40% or less. The solid acidic gas absorbent according to claim 5.

8. A method for separating and recovering acidic gases, comprising an absorption step of contacting a gas to be treated with the solid acidic gas absorbent material described in claim 5 to absorb the acidic gas, and a desorption step of desorbing the acidic gas absorbed in the absorption step from the solid acidic gas absorbent material, wherein the desorption step comprises at least one step selected from the group consisting of (A) applying a reduced pressure to the solid acidic gas absorbent material, (B) contacting it with an inert gas that does not contain acidic gas, and (C) heating it.

9. A moving bed acid gas separation and recovery system, comprising the solid acid gas absorbent material according to claim 5 in the moving bed.

10. A moving bed acidic gas separation and recovery system according to claim 9, which includes a rotating honeycomb rotor as a means for moving the solid acidic gas absorbent, and the solid acidic gas absorbent is supported on the rotating honeycomb rotor.

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