Carbon dioxide adsorbent

Abstract

To provide a carbon dioxide adsorbent capable of adsorbing and eliminating carbon dioxide with lower energy than a conventional adsorbent.SOLUTION: A carbon dioxide adsorbent contains zeolite for which an inclination of a line connecting two arbitrary points of a region corresponding to 20 kPa-400 kPa is 24.08 or more, on a graph that plots results of measuring changes of pressure and adsorption amounts or elimination amounts of carbon dioxide, with the horizontal axis of pressure converted to a natural logarithm, and the vertical axis of adsorption amounts of carbon dioxide.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide adsorbent. [Background technology]

[0002] Carbon dioxide, a greenhouse gas that has the property of absorbing and emitting infrared rays, is known to have an increasing concentration in the atmosphere due to the recent increase in industrial activity. Therefore, in order to prevent the concentration of carbon dioxide in the atmosphere from increasing, an initiative called carbon neutral, which aims to balance the amount of carbon dioxide emitted and absorbed, is being actively pursued.

[0003] As part of efforts toward carbon neutrality, carbon dioxide capture and storage systems are attracting attention, with the aim of preventing carbon dioxide emitted from thermal power plants and other sources from being released into the atmosphere. Examples of systems for recovering carbon dioxide include the PSA method (pressure swing adsorption), which adsorbs by changing the pressure, and the TSA method (temperature swing adsorption), which adsorbs by changing the temperature. Zeolite, a type of clay mineral, is mainly used as the carbon dioxide adsorbent in these systems (see, for example, Patent Document 1).

[0004] Zeolite-based carbon dioxide capture systems often use FAU-type zeolite and are designed using the PSA method. Specifically, carbon dioxide is adsorbed under a vacuum (0 kPa) to atmospheric pressure (100 kPa), and then desorbed under vacuum to separate the carbon dioxide. However, adsorption in this manner requires the use of energy-intensive equipment such as vacuum pumps and high-pressure compressors, which increases energy consumption and the cost of carbon dioxide capture, making it difficult to widely adopt this system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-109818 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a carbon dioxide adsorbent that can adsorb and desorb carbon dioxide with lower energy than conventional products. [Means for solving the problem]

[0007] The present inventors have discovered that by using zeolite that has the property of adsorbing and desorbing carbon dioxide under non-vacuum conditions, it is possible to create a carbon dioxide adsorbent that can adsorb and desorb carbon dioxide with less energy than conventional products. By using zeolite that can adsorb and desorb carbon dioxide under non-vacuum conditions, it is not necessary to use energy-intensive devices such as vacuum pumps and high-pressure compressors to adsorb and desorb carbon dioxide. Therefore, it is expected that carbon dioxide can be adsorbed and desorbed with less energy than conventional products.

[0008] Specifically, the present inventors discovered that zeolites that have the property of adsorbing and desorbing carbon dioxide under non-vacuum conditions are zeolites that, when measuring the change in pressure versus the amount of adsorbed carbon dioxide, have a characteristic gradient in the pressure range higher than vacuum both during adsorption and desorption, and have completed the present invention.

[0009] That is, the carbon dioxide adsorbent of the present invention has the following properties: The zeolite is characterized in that, on a graph obtained by measuring the change in pressure versus the amount of carbon dioxide adsorbed, the horizontal axis represents pressure converted to a natural logarithm, and the vertical axis represents the amount of carbon dioxide adsorbed or desorbed, the gradient of a line connecting any two points in the region corresponding to 20 kPa to 400 kPa is 24.08 or more.

[0010] In the carbon dioxide adsorbent of the present invention, the mass ratio of potassium to sodium (potassium / sodium) contained in the zeolite is preferably 4.70 to 8.70.

[0011] In addition, the carbon dioxide adsorbent of the present invention is The composition is characterized by containing zeolite having peaks at 2θ=27.50° to 27.59° and 28.04° to 28.17° in X-ray diffraction measurement. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a carbon dioxide adsorbent that can adsorb and desorb carbon dioxide with lower energy requirements than conventional products. [Brief explanation of the drawings]

[0013] [Figure 1A] FIG. 1A shows the results of XRD measurement of the zeolite of Example 1. [Figure 1B] FIG. 1B shows the results of XRD measurement of the zeolite of Example 2. [Figure 1C] FIG. 1C shows the results of XRD measurement of the zeolite of Example 3. [Figure 1D] FIG. 1D shows the results of XRD measurement of the zeolite of Comparative Example 1. [Figure 1E] FIG. 1E shows the results of XRD measurement of the zeolite of Comparative Example 2. [Figure 1F] FIG. 1F shows the results of XRD measurement of the zeolite of Comparative Example 3. [Figure 2A] FIG. 2A is a graph showing carbon dioxide adsorption isotherms in the adsorption of Examples 1 to 3 and Comparative Examples 1 to 3. [Figure 2B] FIG. 2B is a graph showing carbon dioxide adsorption isotherms during desorption in Examples 1 to 3 and Comparative Examples 1 to 3. [Figure 3A] FIG. 3A is a graph plotting the results of measuring the change in pressure and the amount of carbon dioxide adsorbed in the zeolite of Example 1, with the horizontal axis representing pressure converted into a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed. [Figure 3B] FIG. 3B is a graph plotting the results of measuring the change in pressure and the amount of carbon dioxide adsorbed in the zeolite of Example 2, with the horizontal axis representing pressure converted into a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed. [Figure 3C] FIG. 3C is a graph plotting the results of measuring the change in pressure and the amount of carbon dioxide adsorbed in the zeolite of Example 3, with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed. [Figure 3D] FIG. 3D is a graph plotting the results of measuring the change in pressure and the amount of carbon dioxide adsorbed in the zeolite of Comparative Example 1, with the horizontal axis representing pressure converted into a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed. [Figure 3E] FIG. 3E is a graph plotting the results of measuring the change in pressure and the amount of carbon dioxide adsorbed in the zeolite of Comparative Example 2, with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed. [Figure 3F] FIG. 3F is a graph plotting the results of measuring the change in pressure and the amount of carbon dioxide adsorbed in the zeolite of Comparative Example 3, with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed. DETAILED DESCRIPTION OF THE INVENTION

[0014] (carbon dioxide adsorbent) The carbon dioxide adsorbent according to the embodiment contains zeolite and, if necessary, further contains other components.

[0015] <Zeolite> Zeolites are compounds whose basic unit is a TO4 unit (where the T element is an element other than oxygen that constitutes the framework) that contains silicon or aluminum and oxygen. Specific examples include crystalline porous aluminosilicates, crystalline porous aluminophosphates (ALPOs), and crystalline porous silicoaluminophosphates (SAPOs). Zeolites are composed of structural units (CBUs) in which multiple (several to several tens) TO4 units are connected. This allows them to have regular channels (tubular pores) and cavities (voids). The zeolite is not particularly limited as long as it can adsorb carbon dioxide and has at least one of the following properties of adsorption isotherm and XRD peak, and can be appropriately selected depending on the purpose. FAU type, PHI type, GIS type, etc. can be used, but PHI type and GIS type are more preferred.

[0016] The zeolite according to the embodiment has the following characteristics in terms of the carbon dioxide adsorption isotherm and the results of X-ray diffraction (XRD measurement).

[0017] <<Carbon dioxide adsorption isotherm>> The carbon dioxide adsorption isotherm of zeolite is a graph prepared by measuring the change in the amount of carbon dioxide adsorbed or desorbed versus the pressure of carbon dioxide while the zeolite is kept at a constant temperature, and plotting the results with the carbon dioxide pressure on the horizontal axis and the amount of carbon dioxide adsorbed or desorbed on the vertical axis. In other words, it is the result of measuring the change in the amount of carbon dioxide adsorbed or desorbed versus the pressure.

[0018] In the zeolite according to the embodiment, on a graph in which a carbon dioxide adsorption isotherm is plotted with the natural logarithm of pressure on the horizontal axis and the amount of adsorption or desorption of carbon dioxide on the vertical axis, the slope of a line connecting any two points in the region corresponding to 20 kPa to 400 kPa is 24.08 or more.

[0019] A graph plotting the carbon dioxide adsorption isotherm with the natural logarithm of pressure on the horizontal axis and the amount of carbon dioxide adsorbed or desorbed on the vertical axis can be created in the following two steps. (1) Create a carbon dioxide adsorption isotherm for carbon dioxide adsorption or a carbon dioxide adsorption isotherm for carbon dioxide desorption. (2) Create a graph by logarithmically converting the pressure in the carbon dioxide adsorption isotherm obtained in (1).

[0020] The method for creating a carbon dioxide adsorption isotherm (a line that graphs the change in pressure versus the amount of adsorbed carbon dioxide) in the carbon dioxide adsorption in (1) above is shown below.

[0021] A 0.1 g sample of zeolite was placed in a high-pressure sample tube (Microtrac BEL Co., Ltd.) and placed in a high-precision gas / vapor adsorption analyzer (BELSORPMAX II, Microtrac BEL Co., Ltd.). The sample tube was then heated and vacuum degassed at 400°C and 1.15 × 10 kPa or less for 4 hours. After the heating and vacuum degassing process, the sample tube was placed in a constant-temperature circulating water bath. The water bath temperature was controlled at 25 ± 0.03°C, and measurements were performed using liquefied carbon dioxide (Chugoku-Shikoku Air Water Inc., purity 99.5 vol% or higher) from 0.03 kPa to 900 kPa absolute pressure. The results were plotted with the carbon dioxide pressure on the horizontal axis and the carbon dioxide adsorption amount on the vertical axis. The plotted points were connected to create a carbon dioxide adsorption isotherm. Saturation adsorption was determined when the pressure change was within 0.1% over 300 seconds.

[0022] (2) above involves creating a graph of the carbon dioxide adsorption isotherm in carbon dioxide adsorption, with the horizontal axis converted to the natural logarithm of the carbon dioxide pressure. Specifically, the horizontal axis is the pressure value converted to the natural logarithm, and the vertical axis is the amount of carbon dioxide adsorption, and the graph is created by connecting the plotted points.

[0023] The method for creating a carbon dioxide adsorption isotherm (change in pressure and amount of adsorbed carbon dioxide) in the carbon dioxide desorption described above in (1) is shown below. In the zeolite that has reached the saturated adsorption amount, the absolute pressure is changed from 900 kPa to 0.03 kPa, and the amount of desorbed carbon dioxide is measured. The measurement results are plotted with the natural logarithm of the carbon dioxide pressure on the horizontal axis and the carbon dioxide adsorption amount on the vertical axis, and the plotted points are connected to create a carbon dioxide adsorption isotherm. When the pressure change is within 0.1% in 300 seconds, it is determined that the saturated adsorption amount has been reached.

[0024] The above (2) is to create a graph in which the horizontal axis is converted to the natural logarithm of the carbon dioxide pressure in the carbon dioxide adsorption isotherm in carbon dioxide desorption. Specifically, it is to plot with the value obtained by converting the pressure value on the horizontal axis to the natural logarithm and the value of the carbon dioxide adsorption amount on the vertical axis, and connect the plotted points to create it.

[0025] <<X-Ray Diffraction (XRD)>> The zeolite of the present invention has peaks (X-ray diffraction peaks) at 2θ = 27.50° to 27.59° and 28.04° to 28.17° in XRD measurement.

[0026] Also, for the zeolite, when the height of the peak at 2θ = 27.50° to 27.59° is A and the height of the peak at 2θ = 28.04° to 28.17° is B, it is preferable that A / B is from 0.27 to 0.40.

[0027] The measurement of XRD is not particularly limited as long as it is a measurement used for the XRD measurement of ordinary clay minerals, and it can be appropriately selected according to the purpose.

[0028] [[ID=二十ー]] The XRD peak position and the value of A / B can obtain a zeolite having a peak at a predetermined position by adjusting the composition ratio of the raw materials, the stirring time when preparing the gel, and the hydrothermal synthesis conditions in the zeolite production method described later.

[0029] The particle size of the zeolite is not particularly limited and can be appropriately selected according to the purpose. For example, if it is the volume average primary particle size, it is preferably from 10 nm to 100 μm, and more preferably from 20 nm to 50 μm. The volume average primary particle size of zeolite can be measured by observing the particles with a scanning electron microscope (SEM). The volume average secondary particle size of the zeolite is, for example, preferably 100 nm to 1 mm, and more preferably 500 nm to 500 μm.

[0030] The zeolite according to the embodiment preferably contains potassium. The potassium content is preferably 13.4 mass % or more based on the total mass of the zeolite.

[0031] The mass ratio of potassium to sodium contained in the zeolite according to the embodiment (mass of potassium / mass of sodium) is preferably 4.0 to 9.0, more preferably 4.70 to 8.70. When the mass ratio of potassium to sodium is 4.0 to 9.0, the zeolite has a slope of 24.08 or more on a line connecting any two points in a region corresponding to 20 kPa to 400 kPa on a graph obtained by measuring changes in pressure versus the amount of adsorption or desorption of carbon dioxide, plotting the results with the horizontal axis representing pressure converted into a natural logarithm and the vertical axis representing the amount of adsorption or desorption of carbon dioxide.

[0032] The mass ratio of atoms contained in a zeolite can be measured by X-ray fluorescence analysis (XRF). In XRF analysis of zeolite, the content of metal species (Si, Al, K, etc.) contained in the zeolite is measured by converting it into the molecular weight of the oxides of these metal species (SiO2, Al2O3, K2O).

[0033] <Other ingredients> The other components are not particularly limited as long as they are contained in ordinary carbon dioxide adsorbents and can be appropriately selected depending on the purpose. Examples include zeolite and activated carbon that do not have the above XRD peaks.

[0034] <<Zeolite manufacturing method>> The zeolite of this embodiment can be produced by a general zeolite production method, which includes a gel preparation step and a hydrothermal synthesis step.

[0035] <<<Gel preparation process>>> The step of preparing a gel is a step of mixing a silica source, an aluminum source, and an alkali metal source to prepare a gel.

[0036] The silica source is a raw material compound that becomes the silicon atoms that constitute the zeolite. Examples of silica sources include fumed silica, silica sol, colloidal silica, water glass, ethyl silicate, and methyl silicate. These may be used alone or in combination of two or more. Among these, water glass is preferred because of its high reactivity.

[0037] The aluminum source is a raw material compound that becomes aluminum atoms that constitute the zeolite. The aluminum source may be, for example, either metallic aluminum or an aluminum compound, but metallic aluminum powder is preferred.

[0038] The alkali metal source is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include Na, K, Li, and Rb. These may be used alone or in combination of two or more. Among these, K is preferred because of its high reactivity.

[0039] In addition to the silica source, aluminum source, and alkali metal, the gel may contain a compound containing an alkaline earth metal, an organic structure-directing material (so-called template), seed crystals, and the like, as long as the effects of the present invention are not impaired. The ratio of silicon atoms to aluminum atoms in the gel is preferably 2.5 to 25.5, more preferably 4.5 to 6.5.

[0040] The gel can be prepared by mixing a silica source, an aluminum source, an alkali metal source, and, if necessary, other components in one step or multiple steps. The order of mixing in multiple stages is not particularly limited and can be appropriately selected depending on the purpose. When mixing in multiple stages, the mixture may be mixed with or without stirring.

[0041] The stirring method is not particularly limited as long as it is a commonly used stirring method and can be appropriately selected depending on the purpose. Examples include impeller stirring, vibration stirring, rocking stirring, centrifugal stirring, and the like.

[0042] The rotation speed during stirring is not particularly limited as long as it is a commonly used stirring speed and can be appropriately selected depending on the purpose, and examples include 1 rpm to 2,000 rpm.

[0043] The temperature in the step of preparing the gel is not particularly limited as long as it is a commonly used temperature and can be appropriately selected depending on the purpose, for example, 10°C to 40°C.

[0044] The mixing time is not particularly limited and can be appropriately selected depending on the purpose, and may be, for example, 5 minutes to 3 hours.

[0045] <<<Hydrothermal synthesis process>>> The hydrothermal synthesis step is a step in which the above-mentioned gel is subjected to high temperature and pressure. "High temperature and pressure" means a temperature at which the solvent boils and a pressure higher than atmospheric pressure. Specifically, this is a step in which the gel is heated in a pressure-resistant vessel to synthesize zeolite crystals.

[0046] The temperature for the hydrothermal synthesis is not particularly limited as long as it is a commonly used temperature and can be appropriately selected depending on the purpose, but is preferably 80°C to 145°C, more preferably 90°C to 140°C, in order to shorten the synthesis time. The temperature of the hydrothermal synthesis may be constant or may be changed stepwise. The hydrothermal synthesis may be carried out while stirring the gel or by leaving it to stand.

[0047] The time for hydrothermal synthesis is not particularly limited as long as it is a commonly used time and can be appropriately selected depending on the purpose. For example, it is preferably 3 hours to 30 days, more preferably 10 hours to 10 days.

[0048] The shape and size of the pressure vessel are not particularly limited and can be appropriately selected depending on the purpose.

[0049] The heating method for the hydrothermal synthesis step is not particularly limited and can be selected appropriately depending on the purpose. For example, a method of covering a pressure-resistant container with a heater, heating in an oil bath, heating in a high-temperature tank, or heating by microwaves can be used.

[0050] The zeolite of the present embodiment may be subjected to a separation and drying step and a calcination step in addition to the gel preparation step and the hydrothermal synthesis step.

[0051] The separation and drying step is a step of separating the solid product from the aqueous liquid after the hydrothermal synthesis step and drying them. The separation method is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include filtration, decantation, spray drying (rotary spray, nozzle spray, ultrasonic spray, etc.), drying using a rotary evaporator, vacuum drying, freeze drying, and natural drying. The zeolite obtained in the separation step may be used as it is or may be washed with water or a predetermined solvent. The drying temperature is not particularly limited and can be appropriately selected depending on the purpose, and may be, for example, 20°C to 150°C. The atmosphere for drying is not particularly limited and can be appropriately selected depending on the purpose. Examples include air, nitrogen, and inert gases such as argon.

[0052] The calcination step is a step of calcining the zeolite, and is often carried out when an organic structure-directing agent is used. The firing temperature is not particularly limited and can be appropriately selected depending on the purpose, and may be, for example, 300°C to 550°C. The baking time is not particularly limited and can be appropriately selected depending on the purpose, and may be, for example, 30 minutes to 3 hours. The atmosphere during firing is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include air, nitrogen, and inert gases such as argon. [Example]

[0053] Next, the present invention will be described with reference to examples, but the scope of the present invention is not limited to these examples.

[0054] (Examples 1 to 3, Comparative Examples 1 to 3) Water, sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.), potassium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.), and an aluminum source were mixed according to the formulation in Table 1. The aluminum source was dissolved during this process. Water glass No. 3 (manufactured by Kishida Chemical Co., Ltd.) according to the formulation in Table 1 was then added and stirred for 10 minutes to prepare a mixed gel. The resulting mixed gel was placed in a stainless steel autoclave (volume: 100 mL) equipped with a fluororesin inner cylinder, and hydrothermal synthesis was carried out at 125°C for 3 days without stirring. After hydrothermal synthesis, the autoclave was cooled with water, and the contents were filtered and dried at 120°C to obtain powdered zeolite.

[0055] [Table 1]

[0056] The aluminum sources in Table 1 are as follows: Aluminum powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Potassium aluminate (Kanto Chemical Co., Ltd.) Aluminum hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0057] The obtained zeolite was subjected to XRD (X-ray diffraction) measurement, and the measurement results are shown in Figures 1A to 1F.

[0058] The XRD measurement was carried out using a measuring device (SMART LAB, manufactured by RIGAKU Corporation) with CuKα radiation under the following conditions. Tube voltage 40kV Bulb current 50mA Measurement temperature 25℃ Measurement range: 5°~90° Monochromatization method with Kβ filter The obtained data was analyzed using analysis software (PDXL2). Data correction was performed by calculating the difference in angle and intensity from the standard Si value and the measured Si value, and correcting the sample value based on these values.

[0059] The results of the XRD measurement, whether or not there were peaks between 2θ = 27.50° and 27.59° and between 2θ = 28.04° and 28.17°, are shown in Table 2. Those that had peaks at these angles are marked with "◯", and those that did not are marked with "X". In addition, when the peak height between 2θ = 27.50° and 27.59° is designated as A and the peak height between 2θ = 28.04° and 28.17° is designated as B, the ratio of the height of A to the height of B (A / B) is also shown in Table 2.

[0060] [Table 2]

[0061] The peak positions shown in Table 2 are those detected in the regions of 2θ=27.0° to 27.7° and 27.7° to 28.8° in the XRD measurement results.

[0062] <Evaluation of carbon dioxide adsorption and desorption> For the obtained zeolite, the change in the amount of carbon dioxide adsorbed or desorbed was measured as a function of pressure to create a carbon dioxide adsorption isotherm. The measurement results for carbon dioxide adsorption are shown in Figure 2A, and the measurement results for carbon dioxide desorption are shown in Figure 2B.

[0063] The carbon dioxide adsorption isotherm for carbon dioxide adsorption was prepared as follows: 0.1 g of each zeolite was placed in a high-pressure sample tube (Microtrac BEL Co., Ltd.), which was then placed in a high-precision gas / vapor adsorption measuring device (BELSORPMAX II, Microtrac BEL Co., Ltd.), and heated at 400°C for 1.15 × 10 -5The sample was heated and vacuum degassed for 4 hours at a temperature of 0.03 kPa or less. After the heating and vacuum degassing treatment, the sample tube was placed in a constant-temperature circulating water bath, and the water bath temperature was controlled at 25±0.03°C. Absolute pressure measurements were taken from 0.03 kPa to 900 kPa using liquefied carbon dioxide (manufactured by Chugoku-Shikoku Air Water Inc., purity 99.5 vol% or higher). The saturated adsorption amount was determined to have been reached when the pressure change was within 0.1% over 300 seconds.

[0064] 2A, the zeolites of Examples 1 to 3 show a rapid increase in adsorption amount at around 200 kPa, whereas the zeolites of Comparative Examples 1 to 3 do not show a rapid increase in adsorption amount at around 200 kPa, and the adsorption amount increases linearly. This result indicates that the zeolites of Examples 1 to 3 have superior carbon dioxide adsorption ability even at low pressures compared to conventional zeolites.

[0065] The carbon dioxide adsorption isotherm for carbon dioxide desorption was created as follows, following the measurement of the carbon dioxide adsorption amount described above. For zeolite that had reached a saturated adsorption amount, measurements were taken from an absolute pressure of 900 kPa to 0.03 kPa without passing carbon dioxide. Carbon dioxide was determined to have been completely desorbed when the pressure change was within 0.1% over 300 seconds.

[0066] 2B, the zeolites of Examples 1 to 3 show a rapid increase in the desorption amount at around 200 kPa, whereas the zeolites of Comparative Examples 1 to 3 do not show a rapid increase in the desorption amount at around 200 kPa. This result indicates that the zeolites of Examples 1 to 3 have superior carbon dioxide desorption ability even at lower pressures than conventional zeolites.

[0067] For the zeolites of Examples 1 to 3 and Comparative Examples 1 to 3, the changes in pressure and the amount of carbon dioxide adsorbed during adsorption and desorption were measured, and the results were converted with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed. The converted results are shown in Figures 3A to 3F. In these graphs, two arbitrary points were selected in the region corresponding to 20 kPa to 400 kPa, and the slopes for adsorption and desorption were calculated. The maximum slopes for each zeolite in this region are shown in Table 3.

[0068] [Table 3]

[0069] As is clear from the results in Table 3, in Examples 1 to 3, in which the adsorption and desorption amounts rapidly increased near 200 kPa, the maximum slope was 24.08 or higher in both adsorption and desorption, whereas in Comparative Examples 1 to 3, in which the adsorption and desorption amounts did not rapidly increase near 200 kPa, the maximum slope was 23.70. Therefore, in a graph in which the results of measuring the change in pressure versus the adsorption or desorption amount of carbon dioxide are plotted with the horizontal axis representing pressure converted to natural logarithm and the vertical axis representing the adsorption amount of carbon dioxide, if the slope in the region corresponding to 20 kPa to 400 kPa is 24.08 or higher, the zeolite has superior carbon dioxide adsorption and desorption capabilities even at high pressures compared to conventional zeolites. This indicates that the zeolites of Examples 1 to 3 can adsorb and desorb carbon dioxide at atmospheric pressure without using energy-intensive vacuum pumps, high-pressure compressors, etc., and are therefore excellent carbon dioxide adsorbents that can adsorb and desorb carbon dioxide with less energy than conventional products.

[0070] In XRD measurements, Examples 1 to 3, which are zeolites having peaks at 2θ=27.50° to 27.59° and 28.04° to 28.17°, have a slope of 24.08 or more in the region corresponding to 20 kPa to 400 kPa on a graph in which the results of measuring the change in the amount of adsorbed or desorbed carbon dioxide versus pressure are plotted with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of adsorbed carbon dioxide. In contrast, in XRD measurements, Comparative Examples 1 to 3, which are zeolites not having peaks at 2θ=27.50° to 27.59° and 28.04° to 28.17°, have a slope of less than 24.08 in the region corresponding to 20 kPa to 400 kPa on a graph in which the results of measuring the change in the amount of adsorbed or desorbed carbon dioxide versus pressure are plotted with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of adsorbed carbon dioxide. Therefore, it can be said that zeolites having a structure in which peaks are present at 2θ=27.50° to 27.59° and 28.04° to 28.17° in XRD measurement are zeolites that can adsorb and desorb carbon dioxide with lower energy than conventional products.

[0071] From the carbon dioxide adsorption isotherms and XRD measurement results of the zeolites of Examples 1 to 3 and Comparative Examples 1 to 3, it is believed that differences in the structure of the zeolites result in differences in the behavior of carbon dioxide adsorption. To investigate this point in more detail, XRF analysis was performed on the zeolites of Examples 1 to 3 and Comparative Examples 1 to 3, and the proportions (mass proportions) of sodium oxide, alumina (Al2O3), silica (SiO2), and potassium oxide in the zeolites were measured. From these measurement results, the mass ratio of potassium to sodium (potassium / sodium) contained in the zeolites was calculated. The measurement results and calculation results are shown in Table 4.

[0072] The XRF measurement was carried out using a measuring device (ZSX Primus II, manufactured by RIGAKU Corporation) under the following conditions. Mode EZ Scan Measurement element range FU Measurement time: 1.4 minutes Measurement temperature 35℃ In X-ray fluorescence analysis, the content of metal species (Si, Al, K, etc.) contained in zeolite is measured by converting it into the molecular weight of the oxides of these metal species (SiO2, Al2O3, KO). Because the content of metal species contained in zeolite is proportional to the molecular weight of the oxides of these metal species, the content ratio of the metal species is the same as the content ratio of the oxides of the metal species.

[0073] [Table 4]

[0074] The mass ratio of potassium oxide to sodium oxide in a zeolite (potassium oxide / sodium oxide) can be considered to be the mass ratio of potassium to sodium in the zeolite (potassium / sodium). In Examples 1 to 3, the mass ratio of potassium to sodium (potassium / sodium) was 4.0 to 9.0, whereas in Comparative Examples 1 to 3, it was less than 4.0 or more than 9.0. This indicates that a zeolite with a mass ratio of potassium to sodium of 4.0 to 9.0 results in a zeolite that has the ability to adsorb and desorb carbon dioxide even under non-vacuum conditions. Furthermore, in Comparative Example 3, the mass ratio of potassium to sodium (potassium / sodium) was 9.4, a value closer to that of Examples 1 to 3 than that of Comparative Examples 1 and 2. However, unlike Examples 1 to 3, carbon dioxide adsorption and desorption were only possible under pressures close to a vacuum. The aluminum source for the zeolites in Examples 1 to 3 was aluminum powder, whereas the aluminum source for the zeolite in Comparative Example 3 was aluminum hydroxide. Therefore, it is believed that the difference in aluminum source is related to the pressure at which carbon dioxide is adsorbed and desorbed.

[0075] Furthermore, in Examples 1 and 2, in which the mass ratio of potassium to sodium (potassium / sodium) was 4.70 to 8.70, the results of measuring the change in pressure versus the amount of carbon dioxide adsorbed or desorbed were plotted on a graph with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed or desorbed. On this graph, the gradient of the line connecting any two points in the region corresponding to 20 kPa to 400 kPa was 55.90 or more. In contrast, in Example 3, in which the mass ratio of potassium to sodium (potassium / sodium) was 4.05, the results of measuring the change in pressure versus the amount of carbon dioxide adsorbed or desorbed were plotted on a graph with the horizontal axis representing pressure converted to a natural logarithm and the vertical axis representing the amount of carbon dioxide adsorbed or desorbed. On this graph, the gradient of the line connecting any two points in the region corresponding to 20 kPa to 400 kPa was 24.08, which is a smaller gradient than Examples 1 and 2. From this, it can be said that when the mass ratio of potassium to sodium (potassium / sodium) is 4.70 to 8.70, the resulting zeolite has the property of adsorbing and desorbing carbon dioxide more effectively under non-vacuum conditions.

Claims

1. A carbon dioxide adsorbent characterized by comprising a zeolite in which, on a graph obtained by measuring the change in pressure versus the amount of carbon dioxide adsorbed or desorbed, the horizontal axis represents pressure converted into a natural logarithm and the vertical axis represents the amount of carbon dioxide adsorbed or desorbed, the gradient of a line connecting any two points in a region corresponding to 20 kPa to 400 kPa is 24.08 or more.

2. 2. The carbon dioxide adsorbent according to claim 1, wherein the mass ratio of potassium to sodium (potassium / sodium) contained in the zeolite is 4.70 to 8.

70.

3. A carbon dioxide adsorbent comprising a zeolite having peaks at 2θ=27.50° to 27.59° and 28.04° to 28.17° in X-ray diffraction measurement.

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