Tailoring activated carbons from Pinus canariensis cones for post-combustion CO₂ capture

Activated carbons (ACs) from Pinus canariensis cones were developed by KOH chemical activation. The effect of the impregnation KOH/carbonized cones ratio (IR = 1, 2, or 3) and temperature (873, 973, 1073 K) on main chemical, textural, and morphological characteristics of the resulting ACs was systematically examined. CO₂ adsorption capacity from gaseous streams was evaluated by gravimetric adsorption tests, and the analysis of breakthrough curves was determined in a packed-bed column at 303 K and atmospheric pressure. Comparison of CO₂ adsorption capacities of the ACs at 273 K and 303 K at equilibrium showed that those samples developed at 973 K with IR = 3 (BET surface area ~ 1900 m² g^-1) attained the highest values (6.4 mmol g^-1 and 1.9 mmol g^-1, respectively), even though the ACs obtained at 1073 K with the same IR exhibited the largest surface area (2200 m² g^-1). Thermodynamic parameters evaluated from CO₂ adsorption isotherms determined in the range 273-333 K for the former sample pointed to a physisorption, spontaneous, and exothermic process; isosteric heat of adsorption was also estimated for the range of surface coverage of the equilibrium isotherms. The kinetics of CO₂ adsorption onto all the ACs was successfully described by the linear driving force model. The breakthrough curves were properly represented by the Thomas' model, the longest breakthrough time and highest adsorption capacity being also attained for the bed packed with the ACs developed at 973 K with IR = 3. Higher CO₂ adsorption capacities of the ACs were directly related to the presence of narrow micropores (< 0.9 nm) induced by the stronger activation conditions. However, an excessively severe combination of the IR and activation temperature exerted a negative influence on CO₂ adsorption onto the ACs, likely due to micropores widening.