Chemical Absorption and Physical Adsorption: Key Roles in Carbon Capture

01 Introduction

Point source carbon capture technology aims to reduce carbon dioxide (CO₂) emissions released into the atmosphere and has become an important solution to address climate change. This article will explore two different carbon capture methods: chemical absorption and physical adsorption, and discuss their characteristics in practical applications.

02  Chemical Absorption: The Foundation of Carbon Capture

Currently, chemical absorption plays an important role in carbon capture, providing an effective means to capture CO₂ from flue gas emitted by power plants, industrial facilities, and other point sources. In this process, CO₂-rich gas flows through a liquid solvent. After the solvent absorbs CO₂, the captured CO₂ is released and separated through thermal regeneration, then stored or utilized.

Commonly used absorbents such as monoethanolamine (MEA) and diethanolamine (DEA) are widely applied due to their high affinity with CO₂. These materials can undergo reversible chemical reactions with CO₂ to achieve capture and release cycles. Absorption systems typically include absorbers, separators, and regeneration units. The regenerated solvent is returned to the absorber for reuse.

Absorption technology using organic amine solvents started early and is relatively mature, with absorption systems capable of achieving high capture rates. However, organic amine solvents undergo degradation during continuous absorption-regeneration cycles, leading to decreased adsorption capacity and requiring regular replacement. Additionally, the solvent regeneration process consumes significant energy, which can cause additional carbon emissions in scenarios without available waste heat, further limiting its comprehensive emission reduction effectiveness. Moreover, the disposal of waste solvents can create new environmental issues. Therefore, in recent years, carbon dioxide capture based on physical adsorption technology has received increasing attention.

03 Physical Adsorption: Carbon Capture Using Porous Materials

Adsorption technology primarily utilizes porous materials such as zeolites, activated carbon, and metal-organic frameworks (MOFs) for the physical adsorption of CO₂. Unlike absorption, adsorption refers to the physical capture of CO₂ molecules by the surface of solid adsorbents, with no chemical reactions occurring during the adsorption process.

Among commonly used solid adsorbents, activated carbon materials exhibit poor adsorption selectivity, resulting in low efficiency and high energy consumption when applied to point-source CO₂ capture. Materials such as zeolites and molecular sieves, in addition to their poor selectivity, also have performance significantly affected by water vapor. Practical applications require additional drying steps, leading to increased capture costs. Furthermore, due to the poor selectivity of these adsorbents, flue gas with low CO₂ content (≤30%) often requires two-stage or multi-stage adsorption to increase CO₂ concentration to over 90%.

Metal-organic frameworks (MOFs) are a class of crystalline porous materials composed of metal ions or clusters connected with Organic Linkers, forming nanoporous frameworks with high specific surface areas and adjustable pore structures. In recent years, a series of MOF materials have been developed that possess high selectivity, high adsorption capacity, and certain water resistance, making them ideal for point-source CO₂ capture. These materials can achieve highly selective adsorption, and even in gas streams with low CO₂ content, they can increase CO₂ concentration to over 90% through single-stage adsorption, making them powerful solutions in carbon capture applications.

MOF-based adsorption carbon capture offers multiple advantages. MOFs have tunable properties, allowing the design of adsorbents specifically tailored for specific CO₂ capture requirements. They can be adapted to different adsorption process systems, such as pressure swing adsorption (PSA) and temperature swing adsorption (TSA). Additionally, MOFs can typically be desorbed at lower temperatures compared to other materials, significantly reducing energy consumption.

04 The Future of Carbon Capture

Recent advancements in the MOF field continue to overcome common limitations of adsorption materials (such as moisture sensitivity and poor selectivity), thanks to their customizable structural design. By fine-tuning the composition and pore geometry of MOFs, researchers have successfully engineered stable and high-performance materials. MOF-based systems can meet standard requirements for efficient carbon capture (95% purity and 90% recovery rate) at different concentration levels, with only minimal desiccant pre-layering needed. This ability to mitigate moisture sensitivity represents a significant advantage of MOFs compared to other adsorption materials like zeolites.

MOFs also exhibit excellent stability and durability, making them popular materials for carbon capture applications. Therefore, the tunability of Mof Structures not only enhances their effectiveness in CO₂ capture but also improves their practicality and reliability under various environmental conditions, further solidifying their leading position in adsorption-based carbon capture technologies.

With global carbon reduction efforts, physical adsorption using MOFs as adsorbents will demonstrate tremendous potential. Researchers continue to conduct ongoing research and development to further improve MOF stability, scalability, and cost-effectiveness, driving their widespread application in industrial carbon capture. By leveraging the advantages of porous materials, we can pave the way for a green and sustainable future for generations to come.

Guangdong Tanyu New Materials Co., Ltd. is China's first technology-innovative enterprise to achieve mass production of MOFs, where hundreds of functional MOFs have been developed. Our team possesses profound technical expertise in MOF synthesis and applications. To learn more about MOF applications and functional customization, please contact our Tanyu expert team for professional solutions.

References

[1]Heliyon, 9 (2023), e22341, 10.1016/j.heliyon.2023.e22341 

[2]Journal of Cleaner Production, 373 (2022), 133932, 10.1016/j.jclepro.2022.133932