Separation of CO2 from different CO2/N2 mixtures using molten salt-derived pelletized activated carbon

In this work pelletized activated carbon derived from pinewood was prepared and evaluated for its potential to selectively capture CO₂ from N₂ in gas mixtures, addressing the need for effective carbon capture technologies. Pinewood was activated at 400 °C with a 60:20:20 mol% eutectic mixture of ZnCl₂:NaCl:KCl. The resulting activated carbon was analysed for its surface chemistry and assessed as a CO₂ adsorbent at different temperatures, pressures and gas compositions. The highest CO₂ adsorption capacity was reached at 25 °C and a CO₂ concentration of 20 V%, with adsorption decreasing at higher temperatures and lower CO₂ concentrations. The Avrami model showed the best fit to kinetic data, indicating the complexity of the adsorption process and accounting for both chemisorption and physisorption. Equilibrium data were best described by the Hill-de Boer model, suggesting the presence of mobile transport on the activated carbon surface and adsorbate-adsorbate interactions. The Z-parameter, accounting for the interactions between adsorbates, was greater than zero, indicating that repulsion between CO₂ molecules occurred. The theoretical selectivity, based on the adsorption isotherms for CO₂ and N₂, reached a maximum of 87.16 for a CO₂ concentration of 10 V%, and decreased with increasing CO₂ concentration. The experimental selectivity, based on equilibrium adsorption data, allowed to account for competition between CO₂ and N₂ for active sites and to investigate the influence of pressure on the CO₂ selectivity. The obtained selectivity's were significantly lower than the theoretical values. The highest selectivity of 13.83 was obtained at a pressure of 861 kPa.