Comparison of CO2 Sorption On Hydrotalcites by Impregnated with Various Alkali Metals

Carbon dioxide (CO₂) is a representative greenhouse gas causing global warming, and adsorption becomes a promising technology among many separation methods to capture CO₂. Inexpensive adsorbents with sufficient CO₂ adsorption uptake for low temperature have been widely developed, but their CO₂ adsorption ability is seriously impaired at high temperature. Thus, it is important to develop CO₂ sorbents for high temperature. Hydrotalcite (HTC), which has been known as an inorganic compound of Mg-Al layered double hydroxide, has many advantages of stable CO₂ sorption, fast sorption kinetics, and easy regeneration over other high temperature CO₂ sorbents. However CO₂ sorption uptake of pristine HTC is not high enough for practical use, thus CO₂ sorption uptake of HTC is usually enhanced by impregnation with alkali metals. So far, most enhancement of CO₂ sorption on HTC focused on using potassium carbonate as an impregnation agent. Other alkali metals such as Li, Na, Rb, and Cs were not systematically investigated.

In this study, HTC was impregnated with various alkali metals in order to enhance the CO₂ sorption uptake and continuous sorption/desorption test was executed for the comparison of CO₂ sorption kinetics and stability of sorbents. Thermogravimetric analysis was used to measure CO₂ sorption uptake and the results revealed that CO₂ sorption uptake on HTC by impregnated with alkali metal was increased in the order of Na<Cs<K<Rb<Li. Also, the analyses based on N₂ adsorption, X-ray diffraction, scanning electron microscopy and infrared spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of CO₂ sorption.