Gas adsorbent

Abstract

To provide a technology that allows for the arbitrary alteration of the shape of the Na-GME type zeolite adsorption isotherm (especially the rise of the second stage). [Solution] A gas adsorbent containing X-GME type zeolite (where X contains Na ions and other alkali metal ions).

Description

[Technical Field]

[0001] This invention relates to gas adsorbents and the like. [Background technology]

[0002] With global warming becoming a global problem, the development of methods for capturing, treating, and utilizing carbon dioxide has become an urgent necessity. While numerous studies are underway in various fields on how to utilize captured carbon dioxide, carbon dioxide capture from the atmosphere is not counted towards the emission allowances set by countries and companies. Therefore, there is a need for highly efficient and low-cost adsorbents that can capture carbon dioxide emitted by economic activities in various sectors, including factories with high carbon dioxide emissions such as thermal power plants and steel mills.

[0003] To date, the amine method, which uses amine-based absorbents, has been considered as a capture system suitable for the large volume of carbon dioxide emissions from large-scale mining and industrial activities. However, it has problems such as maintenance and poor profitability on a small to medium scale. For this reason, pressure swing adsorption (PSA), which allows for easy adsorption and desorption of carbon dioxide, has been considered. However, with zeolite-based adsorbents, the pressure must be reduced to a vacuum during desorption in order to perform efficient adsorption and desorption, which leads to high costs. Therefore, there has been a need for carbon dioxide adsorbents that can desorb with low energy.

[0004] Non-patent document 1 describes that the adsorption isotherm of carbon dioxide by Na-GME type zeolite exhibits a two-step curve. By using such zeolite, carbon dioxide can be efficiently adsorbed and desorbed in a pressure range with low energy costs. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-075419 [Non-patent literature]

[0006] [Non-Patent Document 1] CO2 step adsorption behavior exhibited by GME-type zeolites: Abstract of the 38th Zeolite Research Conference, December 2, 2022. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a technology for arbitrarily changing the shape of the Na-GME type zeolite adsorption isotherm (particularly the rise of the second stage). [Means for solving the problem]

[0008] In view of the above problems, the inventors diligently conducted research and found that a gas adsorbent containing X-GME type zeolite (where X includes Na ions and other alkali metal ions) can solve the above problems. That is, the present invention encompasses the following embodiments.

[0009] Item 1. A gas adsorbent containing X-GME type zeolite (where X contains Na ions and other alkali metal ions).

[0010] Item 2. The gas adsorbent according to Item 1, wherein the other alkali metal ions include at least one selected from the group consisting of K ions, Rb ions, Cs ions, and Fr ions.

[0011] Item 3. The gas adsorbent according to Item 1 or 2, wherein the content ratio of Na ions to other alkali metal ions (Na ions: other alkali metal ions) in the X-GME type zeolite is 95-65%:5-35%.

[0012] Item 4. The gas adsorbent according to any one of items 1 to 3, wherein the X-GME type zeolite has been activated by heating.

[0013] Item 5. The gas adsorbent according to Item 4, wherein the heating temperature is 150 to 400°C.

[0014] Item 6. The gas adsorbent according to any one of Items 1 to 5, which is a carbon dioxide adsorbent.

[0015] Item 7. The gas adsorbent according to Item 6, which is used for the adsorption and desorption of the gas.

[0016] Item 8. The gas adsorbent according to Item 7, which is used for the desorption of the gas at 30°C or higher.

[0017] Item 9. A method for producing the gas adsorbent according to any one of Items 1 to 8, including a step of heat-treating a mixture containing FAU-type zeolite and sodium hydroxide to obtain Na-GME-type zeolite, and a step of ion-exchanging a part of the Na ions in the Na-GME-type zeolite with other alkali metal ions.

[0018] Item 10. A method for purifying and / or separating a gas, including bringing the gas into contact with the gas adsorbent according to any one of Items 1 to 8.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a technique for arbitrarily changing the shape of the Na-GME-type zeolite adsorption isotherm (especially the rising of the second stage).

Brief Description of the Drawings

[0020] [Figure 1] Graphs of powder X-ray crystallography of the powder (Na+-GME) obtained in Reference Example 1-1, the powders (K+-GME and Li+-GME) obtained in Example 1, and the raw material powder (H+-GME) are shown. [Figure 2] Carbon dioxide adsorption isotherms of Na-GME-type zeolite (Reference Example 1-2) and Na / K-GME-type zeolite (Example 2) are shown (activation treatment: 4 hours at 225°C, measurement temperature: 25°C). The vertical axis indicates the carbon dioxide adsorption amount, and the horizontal axis indicates the pressure. In the legend, the content ratio of alkali metal ions in the used zeolite is shown. [Figure 3]This graph shows the carbon dioxide adsorption isotherm of Na-GME type zeolite (Reference Example 1-2) (measurement temperature: 25°C). The vertical axis represents the amount of carbon dioxide adsorbed, and the horizontal axis represents the pressure. The legend shows the activation treatment temperature and time of the zeolite before measurement. [Figure 4] The nitrogen adsorption and desorption isotherms for Na-GME type zeolite (Reference Examples 1-2), K+-GME type zeolite (Example 1), and Li+-GME type zeolite (Example 1) are shown (activation treatment: 225°C for 4 hours, measurement temperature: -200°C). The vertical axis shows the amount of nitrogen adsorbed, and the horizontal axis shows the relative pressure (value obtained by dividing the equilibrium pressure (P) at the time of adsorption by the saturated vapor pressure (P0)). The legend shows the zeolites used. Filled symbols indicate adsorption, and open symbols indicate desorption. [Figure 5] This graph shows the carbon dioxide adsorption / desorption isotherms of Na-GME type zeolite (Reference Example 1-2) (activation treatment: 4 hours at 225°C). The vertical axis shows the amount of carbon dioxide adsorbed, and the horizontal axis shows the pressure. The legend shows the measurement temperature. Filled symbols indicate adsorption, and open symbols indicate desorption. [Modes for carrying out the invention]

[0021] In this specification, the terms “contains” and “includes” include the concepts of “contains,” “includes,” “substantially consist of,” and “consist solely of.”

[0022] In one embodiment, the present invention relates to a gas adsorbent (which may also be referred to as "the gas adsorbent of the present invention" herein) comprising an X-GME type zeolite (where X includes Na ions and other alkali metal ions).

[0023] GME-type zeolites are not particularly limited as long as they are zeolites having a gmelinite (GME) skeletal structure.

[0024] In this specification, the notation "AAA type" (where "AAA" is a three-letter code for the skeletal structure defined by the International Zeolite Association (IZA)) indicates that the zeolite mainly contains the "AAA" skeletal structure. The notation "AAA type" indicates that, for example, 50% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 95% or more of the zeolite skeletal structure is the AAA skeletal structure. The zeolite skeletal structure can be analyzed by powder X-ray crystal diffraction (using CuKα rays (λ=1.5418Å) and operating the copper anode at 30kV and 15mA). The proportion of a certain skeletal structure in the zeolite under test can be calculated from the ratio of the peak intensity of the same peak in the zeolite under test to the peak intensity of the reference zeolite (a zeolite in which a certain skeletal structure accounts for approximately 100%).

[0025] X-GME type zeolite is a GME type zeolite that mainly contains X as a cation that can pair with the negatively charged portion within the GME type zeolite structure. The number of X (cations) contained in X-GME type zeolite is, for example, 50% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, even more preferably 95% or more, particularly preferably 99% or more, and especially preferably 100%, relative to 100% of the total number of cations contained in X-GME type zeolite. The cation composition of the zeolite can be measured by energy-dispersive X-ray analysis (EDX analysis), inductively coupled plasma emission spectroscopy (ICP analysis), or X-ray fluorescence analysis (XRF analysis).

[0026] X includes Na ions and other alkali metal ions. By combining other alkali metal ions, the shape of the adsorption isotherm (especially the rise of the second stage) can be arbitrarily changed. Examples of other alkali metal ions include K ions, Rb ions, Cs ions, Fr ions, and Li ions. Among alkali metal ions other than Na ions, ions with a larger ionic radius than Na ions are preferred from the viewpoint of efficiently adsorbing and desorbing carbon dioxide in a pressure range with lower energy costs. Specifically, K ions, Rb ions, Cs ions, and Fr ions are preferred, more preferably K ions, Rb ions, and Cs ions, even more preferably K ions and Rb ions, and particularly preferably K ions.

[0027] X may be a single type or a combination of two or more types.

[0028] The total number of Na ions and other alkali metal ions contained in the X-GME type zeolite is, for example, 50% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, even more preferably 95% or more, particularly preferably 99% or more, and especially preferably 100%, relative to 100% of the total number of cations contained in the X-GME type zeolite.

[0029] By adjusting the ratio of Na ions to other alkali metal ions (Na ions: other alkali metal ions) in the X-GME type zeolite, the shape of the adsorption isotherm (especially the rise of the second stage) can be arbitrarily changed. In one embodiment, from the viewpoint of efficiently adsorbing and desorbing carbon dioxide in a pressure range with lower energy costs, the ratio is preferably 95-65%:5-35%, more preferably 95-70%:5-30%, even more preferably 90-70%:10-30%, even more preferably 85-70%:15-30%, particularly preferably 80-70%:20-30%, particularly more preferably 80-72%:20-28%, and especially preferably 78-74%:22-26%.

[0030] The Si / Al element ratio of the X-GME type zeolite is not particularly limited, but is, for example, 1 to 500, preferably 1.5 to 100, more preferably 2 to 20, even more preferably 2 to 10, and most preferably 2 to 5.

[0031] In this specification, the Si / Al elemental ratio of the zeolite is as follows: 29 It can be measured by Si NMR.

[0032] The gas adsorbent or X-GME type zeolite of the present invention can be produced by a method that includes the steps of: heating a mixture containing FAU type zeolite and sodium hydroxide to obtain Na-GME type zeolite; and ion-exchanging a portion of the Na ions in the Na-GME type zeolite for other alkali metal ions.

[0033] The mixture may be in solid or liquid form, but is preferably in solid form. The solid mixture contains FAU-type zeolite and solid sodium hydroxide (solid alkali source).

[0034] The cations contained in the FAU-type zeolite are not particularly limited, but are preferably H ions.

[0035] The mass ratio of FAU-type zeolite to alkali source is preferably 1 to 25. By setting it within this range, CHA-type and / or PHI-type zeolite can be efficiently produced. The mass ratio is more preferably 1.5 to 20, even more preferably 2 to 15, and even more preferably 3 to 10.

[0036] The total content of FAU-type zeolite and sodium hydroxide in the mixture is, for example, 70% by mass or more, preferably 80% by mass, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more, on a dry weight basis, relative to 100% by mass of the mixture.

[0037] The mixture can be obtained by mixing each component. The order of mixing is not particularly limited; all components can be mixed simultaneously, or some components can be mixed first, and then other components can be added all at once or sequentially. The mixing method is not particularly limited; for example, various known mixing methods can be applied. Mixing methods can include using particle mixers, Nauter mixers, or methods that involve shearing, such as using a mortar and pestle, ball mill, or mechanofusion.

[0038] The heat treatment is not particularly limited as long as it is carried out in the presence of water or steam. If carried out in a steam atmosphere, the result after treatment is a solid (product (CHA-type and / or PHI-type zeolite)), and there is no need to remove the solvent.

[0039] The heat treatment temperature is not particularly limited, as long as it allows for the formation of Na-GME type zeolite. The temperature is preferably 125 to 150°C, more preferably 127 to 140°C.

[0040] After heat treatment, it is preferable to wash with water. Washing can remove excess alkali sources. Furthermore, drying can be performed after heat treatment or washing, if necessary.

[0041] Ion exchange can be carried out according to or in accordance with conventional methods. For example, ion exchange can be performed by contacting a Na-GME type zeolite with a treatment solution containing other alkali metal ions.

[0042] The total concentration of other alkali metal ions in the treatment solution is not particularly limited as long as ion exchange is possible, but is, for example, 0.2 to 2 M, preferably 0.5 to 1.5 M, and more preferably 0.8 to 1.2 M.

[0043] The solvent in the processing solution is usually water. Other organic solvents may also be included.

[0044] The treatment solution can be obtained by dissolving a compound that serves as another alkali metal ion source in a solvent. Suitable compounds include chlorides, nitrates, carbonates, hydroxides, etc., of other alkali metal ions.

[0045] The contact temperature is not particularly limited, but is, for example, 10 to 50°C, preferably 15 to 30°C.

[0046] The contact time is adjusted according to the temperature and is not particularly limited, but is, for example, 4 to 48 hours, preferably 16 to 36 hours.

[0047] Ion exchange treatment can be performed multiple times, replacing the treatment solution as needed, until the desired ion content ratio is achieved.

[0048] X-GME type zeolite is preferably activated by heating in order to improve its gas adsorption properties. The heating temperature is, for example, 150 to 400°C, and is preferably 180 to 350°C, more preferably 190 to 300°C, even more preferably 200 to 250°C, and particularly preferably 215 to 240°C, from the viewpoint of achieving the highest adsorption amount and a large rise in the second stage.

[0049] The gas to be adsorbed by the gas adsorbent of the present invention particularly preferably contains carbon dioxide. The concentration of carbon dioxide in the gas is, for example, 2 mol% or more, preferably 4 mol% or more, more preferably 6 mol% or more, and even more preferably 8 mol% or more. The concentration is, for example, 10 mol% or more, 15 mol% or more, 20 mol% or more, 30 mol% or more, or 40 mol% or more, and also, for example, 100 mol% or less, 90 mol% or less, 80 mol% or less, 70 mol% or less, 60 mol% or less, or 50 mol% or less.

[0050] By bringing the gas adsorbent of the present invention into contact with a gas, the gas can be adsorbed onto the gas adsorbent of the present invention. The temperature and pressure during contact can be appropriately adjusted according to the gas adsorption characteristics of the X-GME type zeolite used.

[0051] The pressure at contact is, for example, 40kPa or more, 50kPa or more, 60kPa or more, 70kPa or more, 80kPa or more, 90kPa or more, or 95kPa or more, and also, for example, 200kPa or less, 150kPa or less, 120kPa or less, or 110kPa or less.

[0052] The temperature at contact is, for example, 10 to 100°C, preferably 15 to 50°C, and more preferably 20 to 30°C. In another embodiment, the temperature is preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and even more preferably 45°C or higher, and also, for example, 100°C, 80°C, 60°C, or 50°C.

[0053] The gas adsorbent of the present invention can be used for the adsorption and desorption of gases, or for the purification and / or separation of gases by means of the same.

[0054] Desorption of gas can be performed by changing, for example, the pressure and / or temperature after the above contact. From the viewpoint of arbitrarily changing the shape of the adsorption isotherm (especially the rise of the second stage), the temperature during desorption is preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and even more preferably 45°C or higher. Such temperatures are, for example, 100°C, 80°C, 60°C, or 50°C. [Examples]

[0055] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0056] Reference Example 1: Manufacturing of Na-GME type zeolite Reference example 1-1. Hydrothermal synthesis method 1.34 g of NaOH and 26.0 g of H2O were placed in a 100 mL vial and stirred with a stirrer for 5 minutes. This completely dissolved the NaOH. Next, 0.5 g of H-FAU(Si / Al = 2.8) (HSZ320HOA: manufactured by Tosoh) and 2.5 g of H-FAU(Si / Al = 5.0) (HSZ350HUA: manufactured by Tosoh) were added to the vial and stirred for 30 minutes. The stirred solution was transferred to a 50 mL Teflon container, placed in an autoclave, and heated at 130°C for 24 hours. The resulting powder was washed with deionized water. Washing was continued until the pH of the washing wastewater reached 7. After washing, the powder (Na-GME type zeolite) was dried overnight at 100°C.

[0057] Reference Example 1-2. Steam Supply Conversion Method 3.0 g of H-FAU (Si / Al = 2.8) (HSZ320HOA: manufactured by Tosoh), 0.50 g of NaOH, and 5 yttria-stabilized zirconia balls (10 mm in diameter) were added to a planetary mill container (zirconia, 250 mL). The mixture was kneaded at 150 rpm for 30 minutes using a kneader (PULVERISETTE 6, manufactured by Fritsch Japan Co., Ltd.). The resulting mixture was charged separately with 3.0 g of H2O in a Teflon container, placed in an autoclave, and heated at 130°C for 24 hours. The resulting powder was washed with deionized water. Washing was continued until the pH of the washing wastewater reached 7. After washing, the powder (Na-GME type zeolite) was dried overnight at 100°C.

[0058] The crystal structure of the powder obtained above was analyzed by powder X-ray crystal diffraction. CuKα rays (λ=1.5418 Å) were used for the analysis, and the copper anode was operated at 30 kV and 15 mA. As a result, the obtained powder (zeolite) was confirmed to be a GME-type zeolite (Figure 1 shows the results for the powder obtained in Reference Example 1-1 as a representative example).

[0059] Example 1. Production of X-GME type zeolite (X: Na ions and other alkali metal ions) 1.0 g of Na-GME type zeolite obtained in Reference Example 1-2 was added to 100 mL of 1 M alkali metal chloride (LiCl or KCl) aqueous solution and stirred at 25°C for 24 hours (ion exchange treatment). After stirring, solid-liquid separation was performed using a centrifuge, and then the mixture was washed three times with 30-40 mL of pure water. After the washing, the mixture was dried overnight in a dryer at 100°C to obtain a powder. The above procedure was repeated until the desired ion content ratio was achieved.

[0060] The ratio of Na ions to other alkali metal ions in the obtained powder (X-GME type zeolite (X: Na ions and other alkali metal ions)) was measured. + and Na + The content ratio was measured using a Shimadzu ICP emission spectrometer. + The content ratio was measured using a HORIBA energy-dispersive X-ray analyzer (Emax EVOlution). The Emax EVOlution is mounted on a Hitachi High-Tech FE-SEM;S-4800.

[0061] The results are shown in Table 1. X-GME type zeolites were obtained in which the Na ions were substituted with other alkali metal ions.

[0062] [Table 1]

[0063] Example 2. Production of Na / K-GME type zeolite In the same manner as in Example 1, a Na / K-GME type zeolite was prepared by substituting some of the Na ions with K ions, and the ion content ratio was measured. The ion content ratios of the two Na / K-GME type zeolites obtained were as follows: (A) Na + :92.9%, K + :7.1%, (B)Na + :76.3%, K + The percentage was 23.7%.

[0064] Test Example 1. Analysis of Gas Adsorption and Desorption Characteristics The obtained zeolite was analyzed by the gas adsorption method using a measuring device (MicrotracBEL Corp.: BELSORP-max). Before the analysis, the zeolite was subjected to an activation treatment by heating (at 200 °C, 225 °C, 250 °C, or 300 °C for 4 hours). The adsorption / desorption isotherm graphs obtained by the analysis are shown in Figs. 2 to 5.

[0065] From Fig. 2, it was found that for the GME-type zeolite containing Na ions and other alkali metal ions, compared with the GME-type zeolite containing only Na ions, the rise of the second stage of the adsorption isotherm, which is a two-stage step curve, shifted to the high-pressure side. Therefore, the GME-type zeolite containing Na ions and other alkali metal ions can adsorb and desorb carbon dioxide more efficiently in a higher pressure range than the GME-type zeolite containing only Na ions. Further, in Fig. 2, it can be seen that when the ratio of Na ions to K ions is changed, the shape of the curve changes.

[0066] Here, when comparing 100% Na ions with 76.3% Na ions, for example, in the pressure operation from atmospheric pressure (101.3 kPa) to 62 kPa, the amount of CO2 recovered is larger for 76.3% Na ions than for 100% Na ions.

[0067] Thus, by changing the ratio of Na ions to K ions, changes occur in the slope and shape of the adsorption curve. By appropriately setting the range of pressure operation according to the changes, it is possible to avoid CO2 recovery under high vacuum, which requires high energy consumption, and reduce the total energy cost.

[0068] From Fig. 3, it was found that by changing the activation treatment temperature of the GME-type zeolite, around 225 °C (225 ± 5 °C) is a temperature suitable for the reactivation of the GME-type zeolite.

[0069] From Fig. 4, it was found that the adsorption amount per unit weight varies depending on the type of alkali metal ions contained in the GME-type zeolite, and Li +-GME is recognized to have a high specific surface area and micropore volume.

[0070] Figure 5 shows that changing the temperature during carbon dioxide adsorption and desorption shifts the rise of the second stage of the adsorption isotherm, which is a two-step curve, towards the high-pressure side. It has been found that carbon dioxide can be adsorbed and desorbed by swinging the temperature, meaning that carbon dioxide can be recovered not only by pressure but also by a combination of temperature and pressure. In other words, carbon dioxide can be recovered using temperature swing, pressure swing, and pressure-temperature swing adsorption / desorption methods.

Claims

1. A gas adsorbent containing X-GME type zeolite (where X contains Na ions and other alkali metal ions).

2. The gas adsorbent according to claim 1, wherein the other alkali metal ions include at least one selected from the group consisting of K ions, Rb ions, Cs ions, and Fr ions.

3. The gas adsorbent according to claim 1, wherein the content ratio of Na ions to other alkali metal ions (Na ions: other alkali metal ions) in the X-GME type zeolite is 95-65%:5-35%.

4. The gas adsorbent according to claim 1, wherein the X-GME type zeolite has been activated by heating.

5. The gas adsorbent according to claim 4, wherein the heating temperature is 150 to 400°C.

6. A gas adsorbent according to any one of claims 1 to 5, which is a carbon dioxide adsorbent.

7. The gas adsorbent according to claim 6, for use in adsorption and desorption of the aforementioned gas.

8. A gas adsorbent according to claim 7, for use in desorption of the gas at temperatures above 30°C.

9. A method for producing a gas adsorbent according to any one of claims 1 to 5, comprising the steps of: heating a mixture containing FAU-type zeolite and sodium hydroxide to obtain Na-GME-type zeolite; and ion-exchanging a portion of the Na ions in the Na-GME-type zeolite for other alkali metal ions.

10. A method for purifying and / or separating a gas, comprising contacting a gas adsorbent according to any one of claims 1 to 5 with a gas.

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