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JP-2026075861-A - Carbon dioxide adsorbent and method for separating carbon dioxide

JP2026075861AJP 2026075861 AJP2026075861 AJP 2026075861AJP-2026075861-A

Abstract

[Problem] To provide a carbon dioxide adsorbent and a carbon dioxide separation method that have a high effective carbon dioxide adsorption capacity even when the carbon dioxide concentration in the mixed gas is low, when separating carbon dioxide from a mixed gas containing carbon dioxide. [Solution] A carbon dioxide adsorbent comprising a zeolite having a faujasite-type crystal structure, wherein 50% or more of the cations constituting the zeolite are alkali metal ions, the Si/Al ratio is 1.5 or higher, and the Langmuir-Freundlich equilibrium constant determined from the carbon dioxide adsorption isotherm at 25°C is greater than 0.05 (1/kPa) and less than or equal to 0.3 (1/kPa). [Selection Diagram] None

Inventors

  • 針崎 良太
  • 長谷川 泰久

Assignees

  • 住友精化株式会社
  • 国立研究開発法人産業技術総合研究所

Dates

Publication Date
20260511
Application Date
20241023

Claims (9)

  1. It contains a zeolite having a faujasite-type crystal structure, More than 50% of the cations constituting the zeolite are alkali metal ions. The Si/Al ratio is 1.5 or higher. A carbon dioxide adsorbent whose Langmuir-Freundlich equilibrium constant, determined from a carbon dioxide adsorption isotherm at 25°C, is greater than 0.05 (1/kPa) and less than or equal to 0.3 (1/kPa).
  2. The carbon dioxide adsorbent according to claim 1, wherein the Si/Al ratio is 3.5 or less.
  3. The carbon dioxide adsorbent according to claim 1 or 2, wherein 50% or more of the cations constituting the zeolite are sodium ions, potassium ions, or rubidium ions.
  4. More than 50% of the cations constituting the zeolite are sodium ions. A carbon dioxide adsorbent according to claim 1 or 2, wherein the Si/Al ratio is 1.50 or more and 2.75 or less.
  5. More than 50% of the cations constituting the zeolite are potassium ions. A carbon dioxide adsorbent according to claim 1 or 2, wherein the Si/Al ratio is 1.75 or more and 3.50 or less.
  6. More than 50% of the cations constituting the zeolite are rubidium ions. A carbon dioxide adsorbent according to claim 1 or 2, wherein the Si/Al ratio is 2.50 or more and 3.50 or less.
  7. The carbon dioxide adsorbent according to claim 1 or 2, wherein the cation constituting the zeolite consists of only one or more cations selected from the group consisting of sodium, potassium, and rubidium.
  8. A method for separating carbon dioxide, comprising a separation step for separating carbon dioxide from a mixed gas containing carbon dioxide, A method for separating carbon dioxide, wherein the separation step includes a step of contacting a carbon dioxide adsorbent according to claim 1 or 2 with a mixed gas containing carbon dioxide to adsorb the carbon dioxide onto the carbon dioxide adsorbent.
  9. The method for separating carbon dioxide according to claim 8, wherein, in the separation step, carbon dioxide is separated from the carbon dioxide adsorbent by a pressure swing adsorption method.

Description

This invention relates to a carbon dioxide adsorbent and a method for separating carbon dioxide. Carbon dioxide is considered a major cause of global warming, and efforts to reduce emissions are intensifying worldwide. Therefore, various research projects are being actively pursued to enable the capture or storage of carbon dioxide from exhaust gases without releasing it into the atmosphere. Known methods for carbon dioxide capture include, for example, membrane separation and concentration methods, and chemical absorption methods utilizing the reaction absorption of basic compounds. However, currently, both methods have high carbon dioxide capture costs and have not yet reached the stage of widespread adoption. For example, the chemical absorption method requires heating to desorb the absorbed carbon dioxide from the basic compound solution, making it energy-intensive unless it is a large-scale facility equipped with waste heat utilization equipment. Therefore, as a method that can relatively reduce energy costs, the Pressure Swing Adsorption (PSA) method has been proposed for small-scale businesses. The PSA method involves repeatedly performing an adsorption step in which a mixed gas is introduced at a predetermined pressure into an adsorption tower filled with an adsorbent to adsorb a specific gas component, and a desorption step in which the adsorption tower, with the adsorbed gas component, is reduced to a predetermined pressure to recover or discharge the gas component. For this reason, it is considered that energy costs can be relatively reduced. Other methods include Thermal Swing Adsorption (TSA), which separates gases by raising the temperature of the desorption step above the temperature of the gas adsorption step and utilizing the difference in adsorption capacity at low and high temperatures, and Pressure and Thermal Swing Adsorption (PTSA), which combines the PSA and TSA methods. Zeolite adsorbents are widely used as adsorbents in the CO2 -PSA method, which is a PSA method where the specific gas component is carbon dioxide. Zeolite adsorbents are required to have a large difference between the adsorption capacity at adsorption pressure and the adsorption capacity at desorption pressure (hereinafter also referred to as "effective adsorption capacity"), and to have high adsorption selectivity for carbon dioxide compared to gases such as nitrogen. To reduce carbon dioxide capture costs, it is necessary to improve carbon dioxide capture efficiency, especially by increasing the effective adsorption capacity. Furthermore, improving carbon dioxide capture efficiency can also be addressed from a process perspective by widening the pressure fluctuation range, but conventional zeolites have a strong interaction with carbon dioxide, so the degree of depressurization must be increased to achieve sufficient desorption, which increases energy costs. Therefore, to fully utilize the properties of zeolites, it is effective to adsorb high concentrations of carbon dioxide. However, the concentration of carbon dioxide in the exhaust gas of small-scale businesses where the CO2 -PSA method is required is low, and in recent years, the use of cogeneration systems has been promoting the reduction of carbon dioxide emissions, so the concentration of carbon dioxide in exhaust gas tends to decrease even further. Therefore, there is a growing demand for zeolites that have sufficiently high effective adsorption capacity and excellent recovery efficiency, even when the carbon dioxide concentration in the exhaust gas is low. Therefore, in recent years, faujasite with a controlled SiO₂ / Al₂O₃ ratio (Si/Al ratio) has been disclosed (see Patent Document 1 below). Patent Document 1 discloses a carbon dioxide adsorbent containing a zeolite molded body in which the SiO₂ / Al₂O₃ molar ratio is 3.5 to 6.0 (Si/Al molar ratio is 1.75 to 3.0). Compared to conventional zeolite adsorbents, this carbon dioxide adsorbent can increase the effective adsorption amount of carbon dioxide without reducing the pressure to near vacuum, thereby enabling carbon dioxide removal with less energy consumption. Japanese Patent Publication No. 2017-77541 Figure 1 is a graph showing the X-ray diffraction spectrum of the carbon dioxide adsorbent obtained in Example 1. <<Carbon dioxide adsorbent>> The carbon dioxide adsorbent of the present invention comprises a zeolite having a faujasite-type crystal structure, wherein 50% or more of the cations constituting the zeolite (hereinafter also referred to as "main cations") are alkali metal ions, the Si/Al ratio is 1.5 or higher, and the equilibrium constant K of the Langmuir-Freundlich equation, determined from the carbon dioxide adsorption isotherm at 25°C, is greater than 0.05 (1/kPa) and less than or equal to 0.3 (1/kPa). The carbon dioxide adsorbent of the present invention has a higher effective carbon dioxide adsorption capacity compared to conventionally known X-type zeolites, even when the carbon dioxid