Modification of commercial activated carbons for CO₂ adsorption

The aim of the investigations was a modification of DTO, a commercial activated carbon (AC), to improve CO₂ adsorption capacity. The adsorption of CO₂ up to 40 bar at 40°C temperature was investigated. The volumetric method was applied for CO₂ adsorption isotherm measurements. The starting material - DTO - was modified using chemical activation (KOH, ZnCl₂, K₂CO₃). The textural parameters of all the ACs were determined by nitrogen adsorption at the liquid nitrogen temperature of -196°C on Quadrasorb SI. Results showed that the AC modified with KOH had the highest S_{BET}, V_{tot}, V_{mic} values of 2063 m²/g, 1.13 cm³/g, and 0.67 cm³/g, respectively. ACs with a wider pore size distribution (from micropores to mesopores) were obtained. The maximum CO₂ adsorption was equal to 14.44 mmol/g for DTO/KOH - modified carbon whereas 8.07 mmol/g of CO₂ was adsorbed at DTO. The CO₂ adsorption capacities of the ACs were found to be closely correlated with the BET surface areas of the materials tested. The experimental data was fitted to the Freundlich, Langmuir, Sips and Toth equations to determine the model isotherm. The Sips model was found to be the best for fitting the adsorption of CO₂.