K2CO3 함침 활성탄을 활용한 실내 이산화탄소 흡착 연구

Abstract

Carbon dioxide (CO2) is one of the indoor air pollutants, and indoor air quality (IAQ) recommends maintaining the CO2 concentration below 1,000 ppm CO2. In this study, commercial activated carbon (AC) impregnated with low-cost alkaline earth metal oxide (K2CO3) were prepared as an indoor low-concentration CO2 adsorbent. The different amounts of K2CO3 impregnated in ACs were AC (0wt% K2CO3), 25% K2CO3/AC, 50% K2CO3/AC, and 75% K2CO3/AC and their physicochemical properties were investigated using various instruments. The CO2 adsorption performances were evaluated with CO2 adsorption isotherms, thermogravimetric analysis (TGA), and 〖0.1 m〗^3 chamber (CO2 IR analyzer). Based on the initial concentration of 2,000 ppm CO2 in a 〖0.1 m〗^3 chamber, 50% K2CO3/AC showed the fastest CO2 adsorption rate to reached 1,000 ppm with high adsorption capacity at 90.6 〖mg_CO〗_2/g_sample, whereas the pristine AC showed 2.4 〖mg_CO〗_2/g_sample, respectively, which are detected by CO2 IR analyzer. This indicates that physical adsorption by the high surface area and pore volume of the adsorbents and chemical adsorption occur at the same time in the presence of moisture followed by the reaction pathway, R1~R3(K2CO3(s) + H2O (g) + CO2 (g) ⇋ 2KHCO3(s) (R1), K2CO3(s) + 1.5H2O(g) ⇋ K2CO3∙1.5H2O(s) (R2), K2CO3∙1.5H2O(s) + CO2(g) ⇋ 2KHCO3(s) + 0.5H2O(g)(R3)). The proposed pathway and adsorption mechanisms were confirmed through XRD, in-situ FT IR, and TPD-CO2 analysis. The obtained CO2 adsorption equilibrium data were well represented by the Freundlich model, and the adsorption kinetics were treated with a pseudo-second order model, confirming the adsorption controlled by secondary chemical reactions on a reversible heterogeneous surface not restricted to monolayer adsorption Finally, CO2 adsorption/desorption recycling tests were carried out and demonstrated the higher structural stability of 50% K2CO3/AC with a maintenance of adsorption capacity > 95.29% during the ten adsorption–regeneration runs.