Effect of Relative Humidity on Adsorption Breakthrough of CO₂ on Activated Carbon Fibers

Microporous activated carbon fibers (ACFs) were developed for CO₂ capture based on potassium hydroxide (KOH) activation and tetraethylenepentamine (TEPA) amination. The material properties of the modified ACFs were characterized using several techniques. The adsorption breakthrough curves of CO₂ were measured and the effect of relative humidity in the carrier gas was determined. The KOH activation at high temperature generated additional pore networks and the intercalation of metallic K into the carbon matrix, leading to the production of mesopore and micropore volumes and providing access to the active sites in the micropores. However, this treatment also resulted in the loss of nitrogen functionalities. The TEPA amination has successfully introduced nitrogen functionalities onto the fiber surface, but its long-chain structure blocked parts of the micropores and, thus, made the available surface area and pore volume limited. Introduction of the power of time into the Wheeler equation was required to fit the data well. The relative humidity within the studied range had almost no effects on the breakthrough curves. It was expected that the concentration of CO₂ was high enough so that the impact on CO₂ adsorption capacity lessened due to increased relative humidity.