JP-2026075856-A - Carbon dioxide adsorbent and method for separating carbon dioxide

Abstract

[Problem] To provide a carbon dioxide adsorbent and a carbon dioxide separation method that have a high effective carbon dioxide adsorption capacity even under the influence of heat and endothermic heat generated during carbon dioxide adsorption and desorption 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 70% or more of the cations constituting the zeolite are lithium ions, the Si/Al ratio is 1.5 or higher, and the difference in the Langmuir-Freundlich equilibrium constant (1/kPa) obtained from the carbon dioxide adsorption isotherm at 0°C and the carbon dioxide adsorption isotherm at 50°C is 0.3 or less. [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 (6)

1. It contains a zeolite having a faujasite-type crystal structure, More than 70% of the cations constituting the zeolite are lithium ions. The Si/Al ratio is 1.5 or higher. A carbon dioxide adsorbent in which the difference in the equilibrium constant (1/kPa) of the Langmuir-Freundlich equation, obtained from the carbon dioxide adsorption isotherm at 0°C and the carbon dioxide adsorption isotherm at 50°C, is 0.3 or less.
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, wherein the cation further comprises at least one of an alkali metal ion other than lithium and an alkaline earth metal ion.
4. The carbon dioxide adsorbent according to claim 1, wherein the cation further comprises one or more ions selected from the group consisting of sodium, potassium, rubidium, cesium, and magnesium.
5. A method for separating carbon dioxide, comprising a separation step of separating carbon dioxide from a mixed gas containing carbon dioxide, wherein the separation step includes a step of contacting a carbon dioxide adsorbent described in claim 1 or 2 with a mixed gas containing carbon dioxide to adsorb carbon dioxide onto the carbon dioxide adsorbent.
6. The method for separating carbon dioxide according to claim 5, wherein the separation step further includes a step of separating carbon dioxide 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. Activated carbon is widely used as an adsorbent, but it has a low effective adsorption capacity for carbon dioxide. For this reason, zeolite adsorbents are popular as adsorbents in methods such as the CO2 -PSA process. 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. However, it is said that the carbon dioxide recovery efficiency decreases in the PSA method due to temperature fluctuations caused by gas adsorption and desorption. In the PSA method, the heat of adsorption when carbon dioxide is adsorbed onto the zeolite adsorbent generates heat and raises the temperature. This reduces the carbon dioxide adsorption capacity of the zeolite adsorbent. On the other hand, it is known that the temperature drops due to an endothermic reaction during carbon dioxide desorption, and carbon dioxide cannot be sufficiently desorbed. Therefore, in recent years, adsorbents such as FAU-type zeolite, a type of zeolite, and FAU-type zeolite obtained by ion exchange to the Li type have been used (see Patent Document 1 below). Patent Document 1 proposes an FAU in which the SiO₂ / Al₂O₃ ratio is 4.5 to 7 (Si/Al ratio is 2.25 to 3.5), 20% to 90% of the cations are sodium ions, and the remainder are lithium ions, etc. This FAU is intended to separate carbon dioxide with a high selectivity that could not be obtained with conventional carbon dioxide separation agents when separating carbon dioxide from a gas containing carbon dioxide and nitrogen using PSA. Japanese Patent Publication No. 2023-175202 Figure 1 is a graph showing the X-ray diffraction spectrum of the union-exchanged zeolite powder obtained in Example 1.Figure 2 is a graph showing the carbon dioxide adsorption isotherms at 0°C and 50°C for Example 1.Figure 3 is a graph showing the carbon dioxide adsorption isotherms at 0°C and 50°C for Comparative Example 2. <<Carbon dioxide adsorbent>> The carbon dioxide adsorbent of the present invention contains a zeolite having a faujasite-type crystal structure, wherein 70% (mol%) or more of the cations constituting the zeolite are lithium ions, the Si/Al ratio is 1.5 or higher, and the difference in the Langmuir-Freundlich equilibrium constant K(1/kPa) obtained from carbon dioxide adsorption isotherms at 0°C and 50°C is 0.3 or less. The carbon dioxide adsorbent of the present invention has a high effective carbon dioxide adsorption capacity even under the influence of exothermic and endothermic reactions that occur during carbon dioxide adsorption and desorption when separating carbon dioxide from a carbon dioxide-containing gas mixture. Furthermore, the carbon dioxide adsorbent of the present invention can achieve a higher effective carbon dioxide adsorption capacity compared to conventionally known X-type zeolites. The carbon dioxide adsorbent of the present inventio