Influence of oxidation and nitrogen treatment on activated carbon for CO2 adsorption

Abstract

Carbon dioxide (CO2) is the most influential greenhouse gas causing a rise in global surface temperature. The technique for capturing CO2 from post combustion flue gases, namely adsorption, is considered to be a promising technique. Activated carbon (AC) was modified by oxidation in nitric acid and impregnation with branched polyethylenimine (PEI). Oxygen functional groups obtained by oxidation can increase CO2 adsorption performance by electron donating that participates in electrostatic interactions with CO2. Incorporation of nitrogen functional groups can increase the interaction between CO2, as Lewis acid, and nitrogen functionalized compounds, as Lewis base. The effect of the modification steps were studied to understand differences in surface properties by employing X-Ray photoelectron spectroscopy (XPS). The results of impregnation with branched PEI showed that in spite of the increasing in the amount of nitrogen incorporated into activated carbon, the adsorption capacity of impregnated samples was lower than the untreated AC. furthermore, branched PEI was impregnated on oxidized AC, and their CO2 adsorption capacity was slightly higher than the PEI impregnated only samples; however, they still gave lower CO2 adsorption capacity than the untreated AC due to the pore blocking effect. On the other hands, the oxidized only samples gave a higher adsorption capacity as compared to an untreated AC because the presence of more acid functionalities, such as carbonyl and carboxyl on their surface, could promote the CO2 adsorption. In terms of regeneration, both untreated AC and oxidized only samples were easily regenerated, whereas all PEI impregnated samples were regenerated slower due to their chemisorption process.