A technology to improve the carbon dioxide separation performance of zeolite membranes has been developed.
The paper by the research team headed by Professor Choi was published in the international journal Chemistry of Materials.
Possible application in industries related to carbon dioxide emissions.

▲ Professor Choi Jungkyu (left), Department of Chemical and Biological Engineering, College of Engineering, and doctoral student Sungwon Hong (right). 

Recently, a research team headed by Professor Choi Jungkyu developed a technology that can effectively improve the CO2 separation performance of zeolite membranes.
* Zeolite: A material with many micropores composed of aluminum oxide and silicate oxide. Zeolites are known to have over 200 structures depending on the size, shape, and connectivity of its micropores, and these are represented by three-letter codes (e.g., CHA, MFI, LTA, etc.). Zeolite has various uses, such as an ion exchanger, catalyst, and adsorbent.

The research results were published online on May 7 in the international journal Chemistry of Materials (Impact factor: 9.45).
* Paper title: Healing of microdefects in SSZ-13 membranes via filling with dye molecules and its effect on dry and wet CO2 separations

Zeolite is an inorganic porous material with a unique pore structure and a high thermal chemical stability. Due to these characteristics, zeolite has attracted attention as a material for membranes. However, the separation performance of zeolite membranes is significantly lowered due to defects inevitably generated during membrane fabrication that are larger than the inherent pore size of zeolite. As a result, it has been difficult to produce high-performance membranes.

The team developed a post-treatment technique that fills defects in zeolite membranes in a simple and efficient way. It is a method based on selectively filling defects using a dye that is larger than the pore size of the zeolite but smaller than the defect. This is a very economical and simple method of repairing defects in a separation membrane, and it is thus possible to improve the separation performance. The team applied this technique to zeolite membranes with a chabazite (CHA) structure, which is known to be suitable for CO2 separation, and confirmed the improvement in CO2/N2 and CO2/CH4 separation performance.

Carbon dioxide is a typical greenhouse gas that causes global warming. It accounts for more than 80% of total greenhouse gas emissions. Research on carbon capture and storage (CCS) technology for collecting and storing carbon dioxide has been actively carried out to reduce carbon dioxide emissions. Of the various capture technologies, the use of membranes is very promising because it is a small-scale process that is space-intensive and economical compared to other CO2 capture technologies.

In addition, there is necessarily a certain level of moisture in any environment where carbon dioxide is to be captured (such as *flue gas or biogas after combustion). Even a small amount of water can affect membrane performance. While most previous research has been conducted in water-free conditions, Professor Choi’s team, led by Sungwon Hong, a student in the integrated master's and doctoral course, studied the effect of moisture on the performance of and defects in zeolite membranes. The researchers thus identified how moisture affects separation performance.
* Flue gas: the gas produced from the combustion of fossil fuels that is discharged to the atmosphere, particularly combustion in a thermal power plant.

In regards to the significance of the research, Professor Choi said, "This post-treatment technology can be applied not only to the CHA-type zeolite membranes used in this study but also to other types of zeolite membrane, which can contribute to the study of membranes based on porous materials," This research was carried out with the support of the Korea Carbon Capture & Sequestration R&D Center (KCRC) and the National Research Foundation of Korea’s International Cooperation Project.

[Figure Description]  A schematic diagram of the separation behavior of zeolite membranes under post-treatment and moisture conditions.
Only carbon dioxide can be selectively separated after filling the defects in the membrane with the dye (left). When water is present in the injection gas, the moisture acts to prevent defects and thus the selectivity for carbon dioxide is increased (right).