Piperazine-modified activated carbon as a novel adsorbent for CO₂ capture: modeling and characterization

In this study, activated carbon and piperazine-modified activated carbon adsorbents were prepared and used for CO₂ adsorption. The effect of various parameters including adsorbent particle size, adsorbent amount, piperazine weight percent, pressure, and temperature were investigated on the CO₂ adsorption capacity. The adsorbents were characterized using nitrogen adsorption/desorption isotherms and FTIR analyses. The results showed that the adsorption capacity decreases with temperature increasing and increases with pressure increasing. In addition, the surface modification of activated carbon improved the CO₂ adsorption capacity more than the unmodified adsorbent, and the highest CO₂ adsorption was obtained 203.842 mg/g at 25 °C and 8 bar. Additionally, to determine the adsorbent behavior, CO₂ adsorption experimental data were fitted by isotherm and kinetic models. CO₂ adsorption isotherm modeling was studied up to 8 bar at 25 °C, and kinetic modeling was investigated up to 85 °C at 6 bar. The results show that Hill isotherm model and Elovich kinetic models have a good agreement with the adsorption data. Finally, thermodynamic modeling was carried out for modified and unmodified adsorbents, and enthalpy, entropy, and Gibbs free energy changes of adsorption for piperazine-modified activated carbon at 25 °C and 6 bar obtained 17.078 kJ/mol, - 0.039 kJ/mol.K, and - 5.318 kJ/mol, respectively.