CO2 adsorption on chemically modified activated carbon

CO2 adsorption capacity of a commercial activated carbon was improved by using HNO3 oxidation, air oxidation, alkali impregnation and heat treatment under helium gas atmosphere. With Na2CO3 impregnation, this improvement was 8 and 7 folds (20bars) and 15 and 16 folds (1bar) their air oxidized and nitric acid oxidized supports, respectively. [Display omitted] ► AC modification by oxidative treatments, alkali impregnation and heat treatments. ► 8 folds increase in CO2 adsorption at 1bar upon Na2CO3 impregnation. ► High temperature He treatments resulted in further stabilization of the surface. ► Increased aromatization and uniform distribution of Na led by HNO3 oxidation of AC. CO2 adsorption capacity of a commercial activated carbon was improved by using HNO3 oxidation, air oxidation, alkali impregnation and heat treatment under helium gas atmosphere. The surface functional groups produced were investigated by diffuse reflectance infrared Fourier transform spectrometer (DRIFTS). CO2 adsorption capacities of the samples were determined by gravimetric analyses for 25–200°C temperature range. DRIFTS studies revealed the formation of carboxylic acid groups on the HNO3 oxidized adsorbents. Increased aromatization and uniform distribution of the Na particles were observed on the samples prepared by Na2CO3 impregnation onto HNO3 oxidized AC support. The adsorption capacities of the nonimpregnated samples were increased by high temperature helium treatments or by increasing the adsorption temperature; both leading to decomposition of surface oxygen groups, forming sites that can easily adsorb CO2. The adsorption capacity loss due to cyclic adsorption/desorption procedures was overcome with further surface stabilization of Na2CO3 modified samples with high temperature He treatments. With Na2CO3 impregnation the mass uptakes of the adsorbents at 20bars and 25°C were improved by 8 and 7 folds and at 1bar were increased 15 and 16 folds, on the average, compared to their air oxidized and nitric acid oxidized supports, respectively.